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

first of all, i was in leadership positions in most of my E-4 career, .. i had young soldiers like that and i pulled them aside .. do not address matters of such in front of other soldiers .. next of all, if that did not work ,, i involved my immed leader he/she was E-5P &/or E6 (i had both genders for leaders), .. next of all most of times that worked w/ me nearby .. because some Pvts/Pv2s/PFCs/young E-4s had tried to distort the regs, etc. .. one time had to involve the Bn SgtMjr and in days that issue caused a soldier's chapter discharge .. that ruined the ex-soldier's career from better advancements/etc.
a. keep a constant check to make sure younger soldiers are not violated via drugs, or other illicit activities
b. pull soldier aside for to clear issue(s) DO NOT ADDRESS SOLDIER in front of squad, platoon, etc. unless issue(s) involves the whole team, etc.
c. treat soldier(s) with respect, tact, etc. even if they try craziness, etc. occasionally let them vent but make sure they are not endangering their self or others in that respect.

Military members failing to obey lawful orders issued by their superiors risk serious consequences. Article 90 of the Uniform Code of Military Justice (UCMJ) outlines the crime of willful disobedience by a military member a superior commissioned officer. Article 91 covers willful disobedience of a superior Noncommissioned or Warrant Officer. Article 92 conveys what constitutes the crime of disobedience of any lawful order (the disobedience does not have to be "willful" under this article). I would first give them an opportunity to explain why they think they could disobey my command. If there was a valid reason I might reconsider the order then explain the punishment they were going to receive for the blatant disrespect for the chain of command.

A little fan room liberty would be called for.

I had a "Discipline Problem" handed to me from a different department. He had respect for me and my Superiors were impressed that I had him in line. That ended when he back talked our 2nd LT under his breath in front of me. My fellow marines thought I was soft on this guy... until that day. Article 15 was the rule of the day.

Article 15 right up for disobeying a direct order. Recommend max restriction to base restrict all liberty and let it be known that should the individual repeat this behavior that everyone would be restricted to base. The rest of his platoon should instruct the newbe on proper military berring.

Nipped at the bud. I am not the "alpha" person-Dang. I believe drawing a line in the line. Do or see chief or 1st sergeant. . Career at stake.

Back when I was in a little fan room counseling would have been in order. In today's kinder gentler military, that's probably a career killer.

In the old days I would rip their throat out. But being in the kinder gentler Army I would suggest not doing that. But that is behavior that CANNOT be tolerated. Especially in front of the troops. Remember, if they laugh at you in peace time they will laugh at you in war. I would suggest you call that soldier out for their disrespect and immediately after formation you bring the soldier and their first line in your office and take disciplinary action.

I answered this thread not long ago and I can only say that by the answers of alot of the current NCO'S I am SO glad I'm retired. Half my Sergeants because that's what alot of these are if you get my meaning would have been on their way out the door. Tear them up and feed them to their peers was always the best way plus some very strong corrective training that will go a long way hell put might actually learn and be better for it.

Easy... they go to the LPO (E-6) and the LPO tells them what they are expected to do as the E-5 told them and tell them to apologize to the E-5. Anything less than that happens after LPO intervention and they are at parade rest in front of my office after my LPO comes to me.