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

Write them up

I would slap the fuck out of him and demand that he give me a hundred fifty push ups

In the Air Force I would first pull that member into my office and get to the bottom of the issue. I have learned never to jump to conclusions and to know all the circumstances in the member's life. Depending on the circumstances, some form of administrative action is definitely warranted, but mental health or a chaplain may need to be involved as well. However, if after investigating, the member is having a power contest with the superior, I (or a member higher in the chain) would issue a written reprimand with the member in full service dress at attention directing the member this is the member's only warning before the First Sergeant recommends punitive action to the Commander and good order and discipline is expected.

when I first joined you don't talk back to your NCO's or else you will be in the dark side.. I mean extra duty until you get tired.. Not in today's military.

60 push ups and latrine duty for 60 days on first offense

In my day my boot would be so far up is ads he could taste the boot polish

Let your local squad "mafia" do their job,by helping him in his task.Send a BIGGER guy who knows his job.

Request an article 15 if they still have it

take him outside for some fun in the sun...add whatever activity comes mind.

Senior Drill SGT. for 2.5 yrs, an Infantry Plt. Sgt. for 11 yrs. Never had this happen to me. Deportment, and demeanor by a leader will nip this kind of behavior in the bud. But if it did. Sqd.Ldr and I would inform the soldier of a recommendation for an Art. 15. No buts or reasons accepted!