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

Send him to the dentist to get fitted for front teeth.

We cant have flowers protecting our borders

Smoke the shit out of him!

i knock that 2 right off his uniform

Calmly ask him if there's a problem. If he still continues, smoke him until he's swimming

Smoke the shit out of them

I don't care what that person is going through - they have no right to tell an E5 (or even an E4) to shove it.
If the person is having issues with other people in the unit and are getting harassed - or a personal issue has caused them some problems - they need to pull the E5 off to the side and request a private meeting to work something out.

To me, that E2 was ready for a good old fashion ass kicking.

I took my problem child a storeroom and WORKED it out! Never had a issue again.

Push ups, extra duty, restriction, order all hands to assist the individual in performance of the task. No physical touching as you go to jail for that now.

This would depend on what kind of soldier the E2 has been. If this is an isolated incident and kid is going through a rough time I simply do a 4856 because he defied me in front of junior soldiers clearly stating that if this type behavior becomes a pattern will have to follow with UCMJ.
If the E-2 is a proven dirt bag run this incident up the chain of command recommending UCMJ

Make an example out of him and assign him some one else's task as well for being a smart ass

The pen is mightier than the sword so Article 15 that butt

Lose my freaking mind

Make him wish he had kept his mouth shut

I would make all of the other recruits responsible for his disrespect

Combat medic badge. I took the test as enlisted but earned my wreath ad a nurse 0-2

Ooooo Lord!!! Request UCMJ action, Take his precious time n enjoy watching him on shit details

Being a commissioned officer, probably just delegate dealing with it to my most senior NCO as that would be his lane.

My first reaction would be to smoke him in place. If he refuses, turn the formation over to the next ranking NCO and w/said troop's NCO/SP4 move aside; lock him up, and inform him in no uncertain words how badly he is fucking up. Then I would have smoked him repeatedly. If he refused to be dealt w/in such a manner I would write him up and take his rank, money, and time for as long as the CO would allow.

Of course that was when I was in some 14 years ago. Now I'd not smoke him but take rank, time and money from him. You crushed shit like that ASAP or it ruins your own position and sets the stage for more problems.

My question though is why? Have you been overly nice to him or other privates? Is he a problem child? Do you not spread the evil details around to all or just some? In my 22 years I never saw a troop pull that in any unit I served in though admittedly they were mainly line or airborne infantry units where discipline was strict.

I would handle it the same way I handle insubordination at work. I would ask him and the Leading Seaman to stay behind for a moment and "have a conversation", documenting the event...If there's something hidden at home or medical going on I'll try to be sympathetic, but firm about the importance of following orders.

As The Doctor (Doctor Who) says..." No second chances", if they've done it before and there's no medical or other extenuating circumstance at play, they are about to go have a talk with my supervisor and I, who may decide that a trip to the Division Officer is required.

But then again I would never assign someone something that I would not have done myself and chances are as an E-5 I may be working right along side of them anyway doing other things I have on my list from the E-6 or E-7...