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

Insubordination at any level should be dealt with immediately. Though new precedent looks to be happening in real time on full public display by a Secretary and a Admiral.

After the remark is made ,oh ok you stand right there once formation has been released.
This soldier would be my shadow until I got tired of it three weeks a month two months what ever it took.
I would give it 2/3 weeks never Speaking a word of what they did but now permanently reassigned to me and my duties until further notice. When I was ready we would have a conversation about what had a occurred that morning.
Look they do not want to follow you around all day having them report to you. It's the last thing they want it obvious they have an issue with you or authority or something they have just broken the secret understanding do what I order you to do without hesitation. If they can not follow well you get the drift.

I would give it a few good weeks and then sit with them and get to the bottom of why they thought that was a good maneuver that morning. I am sure by now they wished they didn't even know how to talk that morning.

They would be so ready to get back to a normal duty day without you attached to it.
I would still have them with me for an extended time even after I felt we had corrected this issue, All meals extra duty , extra PT.
I would be right there all day everyday until I was sure this was fixed and once we both now back to a normal duty day I can see what we have done together.
Hopefully for my effort I have made a better soldier a better person maybe even now they know they are worth the effort that is the job of a NCO .

You can punish any time A15 all day long it does not solve a thing and should be your very very last resort with a E3 and below.
But getting someone to look at the days duties as a privilege is what your after. It's called Service and that means sometimes helping those who volunteer find their way and sometimes that requires something different than an antiquated punishment system that is thrown down way to soon and often if you make it to SGT do your job.
Everyone has a Pen !

As a former platoon sergeant of many years I would have slugged a son of a bitch in the stomach if it can't take that shouldn't be there

I think you mean PVT (E1) Smart Mouth who will find himself short 7 days pay at the end of the month and very busy after normal duty hours for the next 14 days. If there was something going on that I was unaware of my 1SG will let me know so "WE" can get him whatever assistance needed while he serves his punishment. But those junior leaders represent me and they will not be disrespected.

You make them into an E-1 with your commander’s help... that should do the trick.

It would never happen and didn’t in 21 years.

Up the chain of command

This is a situation that demands low fragmentation damage. PLT SGT." SQD LDR remove the PVT from the formation and escort him to the Orderly Room I will be right behind you." Pass out the rest of the jobs and information. Move to the Orderly Room. Discuss it with SQD LDR and Soldier, tell both what you think should be done for the violation My recommendation would be UCMJ, Ask the SQD LDR what their Recommendations are, Move forward to paperwork if needed. (Counseling as a minimum) Never have this kind of chat without counseling Paper work good or bad. Go Back to work. If you made it through BCT. You know better than that type of conduct. Just my thoughts.

LMAO...…"Corner Patrol". A friend of mine used this with some of his more "stubborn" cases. He would place the offender in a corner, facing inward. Their choices were to watch the corner or report to the Master At Arms. No movement or talking They were not required to stand at attention, but they were to remain standing. He would place a sign next to them with the words, "For information regarding this individual contact ********** Do not speak to or approach." He would simply tell them "When you're ready to act like a useful person, let me know." He would walk by once an hour and ask them if they were ready yet. It seldom took very long. Only one time did an Officer ever inquire about it. After that they were very careful to "Not see" the few times he used this approach.

Well you have three options here.

The FIRST thing i would do regardless of the the other three are push ups as an on the spot correction. And if he refused to do that I would immediately go to option number 2.

Option 1. smoke session, after hours.

Option 2. Formal counseling, and smoke session after hours.

Option 3. Article 15 disrespect to an NCO, and Violation of a lawful order (1 count for refusing the assignment, 2 if he refused the push ups).

I would also counsel the soldier informally, to see where he stands. If he is flippant in the counseling session I would make it a formal counseling session. I would also immediately log the insubordination in a log book (you will need this later).

There are three things that could be happening here:

1. The Soldier is not used to Garrison life, because he just came off AIT, and he may be a little burnt out. This happens, it happened tome in the Navy my A School was 9 months long, then i had 10 weeks of fligth crew training. It took me about 6 months to relax from the training environment, which was very hard on me, because I had A LOT of issues when i first joined the Navy.

2. He is feeling out the waters, trying to see if he can walk all over you, and he may not be fully aware of what is going to happen to him. He may not understand that he has violated the UCMJ, and what those punishments can be. That is why I would counsel him informally. Explain to him that an Article 15 can result in confinement up to 30 days, loss of rank, and a fine of half his pay for 6 months. And that further disobedience can lead to a Bad Conduct Discharge, and that this is his first strike in that regard.

3. He may have decided Army life is not for him, and as such he may be looking to get discharged. He may be a barracks lawyer, and think he is going to get off with an administrative separation and an other than honorable. I would NOT let this happen. He signed the papers, he asked to be there, and now he wants to go home? I would send him home with a Big Chicken Dinner.

I would check with legal, i am not sure exactly what has to happen but i think two or more article 15's in the space of 6 months can be used as a BCD. I would definitely document everything disrespect, refusal to obey, and lack of performance; this is going to be very important too, as there is a malingering charge in the last article of the UCMJ. And then I would article 15 him the two times, and then on his third infraction and I would court martial him, and give him the BCD.