How would you react to an E2 who "smart mouths" you in formation?

Are they still in formation until subject in question has complied?

Simple...Article 15

Sand pile at location A, one bucket in hand 1 and one bucket in hand 2, relocate sand pile from location A to location B, using only the two buckets, an E Tool and your own strength....THEN, after the sand pile is moved, the Commander realizes that it is in the wrong place and needs to be relocated again. after moving 2 tons of sand two buckets at a time 4 or 5 times, you could order him to go find a left handed Torque Wrench with a camo handle and he will sound off with Yes, Sergeant

This answer seems cut and dried, as in that's what you do to this poor PFC's keister. Enlisted matter; don't bother the Officers and CERTAINLY don't bother the CO.

Very well. Moreover, I (as a Sr. Grade Officer) would understand this.

Now, here's where I would like to go "above and beyond." PFC SelfHypnotizedImportantTurd (note acronym) has done what some of us in the business call "acting out." As a Sr. Ranking Officer (and very likely CO or Deputy) I become interested in the "Why's" of these things.

So, number one: I would like to know when such things happen in my unit. (Let's say I'm in the CO role, here)

Number two: I would like to know how it was handled (this is not to judge, simply to observe that the process was followed).

Number three, I would like to know if PFC SelfHypnotizedImportantTurd would like to consider a change of attitude. As an initial action, I would ask the opinion of the NCO leadership.

Number four, I would like to see if there was anything in PFC SelfHypnotizedImportantTurd's life that would trigger such behavior, and is there anything that could be done about it (one might be surprised).

Number five, I would like to know PFC SelfHypnotizedImportantTurd's intention regarding his career; does he want to continue in the US Armed Forces (anywhere, including the NG, etc.). Again, at this point I would get a report from the NCO leadership.

Number six, I would like to chat with NCO leadership about PFC SelfHypnotizedImportantTurd. This is not to make any judgements on this PFC, or the NCO leadership, but to simply gain some intel on the matter. As the CO, the entire unit is my responsibility; if something is happening that is causing PFC SelfHypnotizedImportantTurd's momentary insanity then I need to know, enlisted matter or not.

Number seven, I would want to review any/all corrective actions. Again, this is not to judge but to simply observe that the process was followed. Okay, I might judge if I think things could be done better, but (because it's an Enlisted matter) I would want to consult with the NCO leadership.

Number eight (finally), I would like to see if a chat with PFC SelfHypnotizedImportantTurd might produce any results. I would approach it matter-of-factly. No raised voices, no threats, no promises. Again, it's my job (as a CO) to see to the effectiveness of the entire unit; a "disturbance" of even one member is not too small a detail to ignore. The inputs of my NCO leaders would be fresh in my mind, and I could see about getting any insights into the situation. If PFC SelfHypnotizedImportantTurd wants a career change, it could be easily accommodated. If PFC SelfHypnotizedImportantTurd would like to continue with the DOD (it's a great career!) then I would like to see if some agreement could be reached. (Agreement, as in you need to cut this crap out or we'll cut your crap out of this unit. Sorry, not negotiating at this moment. Your unit supervisor will have some duties for you. Do them. We can chat later if that all works out.)

Well, as long as this assignment is not unethical amoral and is not in violation of any regulations, it’s a lawful order from an NCO. The private will face the consequences if he/she refuses to obey.
My first reaction will be: “Private, I thought that I was a little bit flexible on whom I was going to give this tasking to, but thank you for volunteering. I will give him/her the 5W’s and move on. If SM fails to obey, I will write his negative counseling and begin with his/her chapter process though the chain of command.

Remove him from the formation. Leave him standing, far enough away that he can’t be heard. Leave him there until you have completed the formation. Stay with him there until everyone else is gone. Leave him there while you talk to the 1Sg about his future in your Army. He should still be a formation of one. He is not to leave formation without first getting your approval..

"Drop and give me 50 push-ups"! Extra duty, maybe! Report this E2 to the ISG for an attitude adjustment!

In front of God and Laudy Doddy and everybody I have him in the front leaning rest position and stay there till I’m done with my formation then dismiss every one except Pvt tent peg, then I would get down in his face while he is doing push ups , and tell him in no uncertain terms that he is a POS ( no one hears that but him) then I would get up and tell him to go to the start position and hold it, I would have a phone conversation with a friend then tell him to start pushing till I am tired,,,, he will be down their for a good 30 minutes before I have him recover, then I would lean into him and tell him “ am I hurting you “? No Solider I am conditing your mind and body to help you pass your APFT, now yell that back to me,,,, “ Thank you 1SG for conditioning my mind and my body”,,,,,,,,, DISMISSED

If you’re the first line supervisor, have a conversation with your squad leader and discuss the situation. Seeking assistance from your chain of command helps you grow at the same time of the soldier.
What was the source of this soldier’s rank to E2 Was it awarded to him prior to BCT?
The outburst needs to be addressed, a counseling at a minimum. It’s also an opportunity to see his reasons. Has the assignment been given over and over has he had conversations with you about why? Is the assignment busy work or mission critical?
Lastly how his other responsibilities? Is his room, bunk, uniform, PT scores in line? Does he have an E4 or E3 punishing or smoking him. Is He looking for a failure to adapt or just wants to get out?
Remember or understand the leadership principles of praise, correct, praise, remind him of your open door to discuss offer to destroy counseling form if he has not other outburst in 6 months or so.

I was an E-5 during my deployment in Vietnam and the people I worked with for the most part were highly trained professionals of the same rank as myself.

Prior to this however, we didn't have time for momma boy, lolly gagers that wanted to disrupt the flow of things for everyone else.

Was there corporal punishment? You bet! You either got with the program or you got out of my beloved Army. Lives depended on what we were doing and I had no patience for insubordination of any kind.

RU kidding me.... I would make sure that Seaman X would remember that day for the rest of his life.

Well...... in today's Military I wouldn't be surprised that would happen. Not at all. My last few years Active Duty we joked in the Wardroom that "We" must adopt to them via "Them" adopting to Us. And only once when I was a W4 a E-9 smarted off to me and I took care of that shit real quick.

Oh, I was hoping this would be a senior E-5 (though Senior E-4 would equally count...)!

First response would be, "Excuse me?" followed by "Did I hear you correctly, Seaman Apprentice?", followed by "Ok, no problem, Let's go see what Petty Officer First Class/Workcenter Supervisor has to say after we're done here. Perhaps a private chat is in order about your problem with my orders."

I’m not trying to criticize anyone because everyone has different leadership styles. One technique would be to immediately put that individual into a thinking position…elevated push-ups, mountain climbers, burpees, etc choices are endless. You do this to regain control of the situation, because when he tells you no in front of everyone you have evidently lost control. While he is busy thinking you continue with your information dump. Once complete you release everyone but him then you take him off to the side along with his team leader and explain the consequences of being insubordinate. I have found throughout my career that a good stern corrective talking and some physical coaching goes along ways. If that doesn’t work they sure hate to loose their personal time and money… that requires constant and repetitive counseling. I know things have changed since my time you have to figure out what works best for you. But I can tell you if you wait one minute to correct it you just lost respect of others as well. Good luck. My recommendation nip it in the bud immediately with a swift corrective action. It shows you will not tolerate it. That’s why you talk to him afterwards it shows empathy and understanding.

You are an E-5, senior or not. You are an E-5 speaking to an E-2. If I were you, there would be 2 paths I would take. The first is EMI to get the E-2's attention. The second is placing the E-2 on report for blatent insubordination. There is no way this type of behavior can be tolerated. But there's something else I'd be concerned about. This dirtbag has been in less than a year and he mouths off to his/her E-5.
I'd have to look at the E-5 and their leadership skills and ability as well.

GySgt is right. The old saying goes, reward in public, reprimand in private. However, one of my big faults we’re letting it go at that moment. I’ve been in this situation before and I can tell you that I had an immediate response. There was no way me being a SFC and being talked to by an E-2 like that and I waited until nobody was around .

I have been a squad leader, a platoon sergeant, and a section sergeant. . To me , there’s only one way to handle this, I’m going to rip him/ her a new one. Today’s Army seems to be kinder and gentler,

Wall to Wall counseling. That bullshit from an E 2 is completely unacceptable. He is not gonna have that shit fly

Like a "Ball of Fire!" first, he would be doing pushup until he moved the base to a more pleasant area. Then there is remedial training/extra training, that can be conducted on off duty time so long as an NCO is present and conducting this in the area of their failure, and you can do this for as many days as you wish. You are allowed to do this under the regulations that gives you the power to do so.
The training has to be with in the area of the infraction. Like out to address a superior and how to conduct the task they are assigned like mopping the hall. Then repeat the training how to address an superior and carry out the task they are assigned. you can repeat this as many times as you wish so long as an NCO you are present, and you are the one conducting the training.
This is what Real NCO's do. You don't hand out recommendations of ART-15s like tickets on the speedway. Your job is to train them in their short comings. When you do this, things in your squad or team start changing, the whole starts to work as a team, you have to train the people you get for these are the same people you're going to go into conflicts with. Plus, your command will have more respect for you. Because you are willing to take your time to train your people. So, I say, "Smoke their ASS!" like you are "The Fire Ball from Holy Hell!"
Remember You are an NCO and NCOs have no off duty time!

Burpees until they puke and then have them do the task