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

I would assign him the most demeaning task I could think of, cleaning the toilets with his bare hands, scrubbing the floor with a toothbrush. Something like that.

I’d kick his ass in front of the platoon. But, that is me. A more disciplined Marine NCO would virtually take Pvt Shitbird apart with commanding rhetoric and an overwhelmingly dominant attitude.

Promote to E-4 mafia

Crushing his soul my be in order. However, is this a first offense? If it is, a heart to heart in the PSG's office with the platoon sergeant and platoon leader is in order. The Soldier needs to understand insubordination and the consequences, and it needs to be on paper. Make sure the kid knows that it's serious and that the counselling has the magic bullet in it. If it isn't . . . Well, time to start crushing souls. I typically start with summarized and work my way up from there. Most joes get it when their time is taken with out the need to go after pay and rank. If they don't . . . That rank and pay is going with more of their time.

How the hell did he make it that far. If he has been in that long and with that attitude he did not just wake up and decide to be an idiot. I was a Marine, in my experience he would not have made E-2. As a corporal and squad leader, at various times when I got a new guy I checked his background and past performance. He didn't just walk out and report in. If by chance he did just get assigned and I wasn't informed until he was standing there his new fire team leader would meet him first. Usually it was the Fire Team Leaders and myself in a meeting. I told them what I wanted done and they told their team. IF for some reason I had to do this as a squad the minute he opened his mouth he would be standing at attention by himself off to the side while I finished. His new fire team leader would assist in addressing his problem and develop an attitude adjustment procedure. Of course the team leader and myself would be discussing in front of the miscreant whether to have a blanket party, have him run in full gear around the barracks for an hour or two. Probably settle on scrubbing the latrine with a tooth brush after lights out. The only thing the rest of the squad knows is that this young man opened a can of "Ohhh, Shit." Let their imaginations run with it.

If this is his first offense it would be handled differently than if my wonderful Platoon Sgt decided he liked how I instilled leadership and a spirited and effective work ethic in my Marines. A lot of variables involved. Take you pick on how to handle.....

Remove them from formation and they can do pushups til formation is over, then a week at KP duty

Better yet, a brand new E-2 arrived in my unit. I returned from some meetings to find the coffee pot empty. The Operations Sgt was out. I directed The E-2 to make a pot of coffee. I took the time to instruct him on the task. Pvt. informed me his Drill Sergeant told him he did not have to make coffee for anyone. Mistake 1: He did not stand when I entered the room. 2. He did not address me as even Sergeant when he refused. Result and solution: Everyone in the Orderly Room drank the COFFEE I brewed before a fresh pot was made. Pvt. after that day never failed to acknowledge his 1st Sgt or refuse any task issued by a NCO. I never inquired about the conversation The Operations NCO had whith him. I do know my Ops Sgts ass was on fire after he departed my office.

Drop his whole squad. If he doesn't drop, then drop the whole platoon.
If that doesn't do the trick release the platoon then counsel him on his behavior and let him know that you will put an Article 91 in his file for insubordination.

I'd have him report to the orderly room and wait for the 1sgt, CO, and myself and tactfully remind him of UCMJ and then negatively counsel him for insubordination and let him know that if this attitude continues then I'll push for Art 15 and bad conduct discharge

Whoop his ass or make him do bends and thrust till I was tired..

IMMEDIATELY get in their face, lock them into parade rest, and confirm that they are receiving a direct and lawful order. Army regulations (contrary to belief) authorize a reasonable of physical “coaching “ to get him to comply. After that, the PSG, and as a last resort, the 1SG, should be involved. A counseling statement can be used, as well as recommendations for Article 15.

The NCO should be firm, professional, and SWIFT. Otherwise, every troop around will think they can get away with it. Every NCO witnessing the event should band together and put this young turd in his place.

Conjour up a page 11 right then and there

I will mass punish the entire platoon to the pint of feeling dying, but just the platoon, not him, then I make sure everyone understand that every punishment is his fault. I will cancel passes, leaves, and every single time off. I will get them every single detail...at the end, he will feel it either way.

Take sworn statements and push for UCMJ under Article 92. Meanwhile, I'd find as many meaningless, menial tasks for said private to perform until he or she recognized the fact that I am the authority figure here.

After he gets up off the floor,you tell him again! Then put a boot up his sorry ass,that is the way it was done in the army before,

In the "Old Days" it would have been - Fall Out Private and report to the PSG/Plt Ldr's Office, after we fill out your Counselling Statement for Disrespect and Failure to Obey. Of which the E-2 could possibly lose his "free time" (extra training or extra duty) for several weeks, possibly forfeit some money, and quite possibly go back to being a "Slick Sleeve" Private.

From an Army perspective I have to say the information above is not complete enough for me to really judge. My old man was in the service and was all sorts of combat arms in Regular Army and National Guard. My Mother was an Army Reserve LTC running Selective Service with a joint service command. I did Intel. The military is a huge world, and the branch/unit matters...and in this case where it matters is in understanding the soldier in front of you, and those around them. Where I was stationed we almost never saw an E2 (you had to f-up in AIT not to leave as an E3 because of the length of training). Also if you make PV2 dipshit late for work, you are screwing COL OwnsYouBNCDR's ASS by depriving them of 10 minutes of that soldiers time. Further more it was a very cerebral area. Days of PT is not an option. I say this to hopefully break what I read as a chain of very high-school bully oriented knee-jerk reactions.

What is certain is this. The Soldier needs a hard correction. The correction needs to be measured, because if you cannot measure a response then you are unfit for command, or authority. The NCO needs to know his unit well enough to be able to determine if this is a one off/single point of failure scenario in which case you discipline privately...or if it is a culture thing you make the correction to the offending private, but you do it in public where all can see the consequences.

I would also hope the NCO's next level up would take the situation as an occasion to do a pulse check with his unit to see if there are larger problems that needs addressing to include the possibility that the NCO had been conducting themself in such a way as to create the tension.

This one is simple. In front of yours troops, you explain to the dip-shit that this is not the play ground, that you expect him to behave in the same manner as the other troops. And since he does not appear to understand how things are done he can chose between some extra military instruction ( you still have that tool I hope ) which will consist of cleaning a few choice items with a tooth brush, to your satisfaction, during what would have been his normally free time that weekend, or standing tall in front of the person who can issue punishment under the UCMJ.
I say in front of the troops because he smart mouthed you in front of them, and they need to see the results, or they too may start to believe that they can slack off.

Pube patrol

Smoke his ass, if he doesn't care about that kind of stuff, NCOs have authority under UCMJ so if they're not recognizing it, a commander can slap him with extra duty or reduced pay. That kind of disobedience is toxic and has the potential to hurt readiness. find a creative punishment that wastes his free time. If you're his first line leader, unfortunately wasting his time usually means wasting yours. If you're his SL, have his TL supervise some of his corrective training to spread the workload.