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

write his /her ass up Then this response would be adequate..."Pvt Numbnuts you will stand by after formation." Proceed with the assignment of duties for all others and break formation. "Pvt Numb, have you lost your effin' military mind?!?" There should be an immediate response. Followed by either some PT and then numbnuts going about his duties as ordered or counseling with the Platoon Sergeant present and paper trail of said counseling.

When I was in we never dared. Consequences were brutal

I tel him he signed up and these are his orders to carry out

Being a Mustang, my opinion is that you ignore the second bad mouth, dismiss the troops and see the PVT in private with another NCO present. Your first approach, as a counselor, is to be supportive. Ask how the PVT feels. What's going on in his life? Is anything bothering him, etc. Rule out illness, drugs, alcohol, personal tragedies, financial problems, etc. Those things aside, ask the PVT what he would do with an insubordinate troop if he were the NCO. The discussion, if the PVT is calmed down and being rational, should lead him to the understanding that what he did was wrong on many levels. It was unprofessional, disloyal, against the values of the military and not in keeping with the traditions and purpose of the military. There should be punishment and a requirement for a public apology. Face-to-face show downs are never as successful in reality than as they are in the movies. Troops lose respect for a supervisor who looses it on a Troop, even if the Troop deserves it. Praise in public, discipline in private almost always yields the best results. Demonstrating calm leadership in the barracks translates to battlefield confidence. If you lose it when there are no billets flying, what are the troops expected to think about your battlefield leadership ability?

Slap them!

Start by giving them the worst assignment possible. If that does not work then restrict them to base.

Early on in my E5 rank I smoked guys like this. They straightened up after that. Later on I was in my 1Sgt's office with my E7 being told we cannot smoke joe no longer. We have to counsel them instead and let a 45/45 be their punishment. IMO, smoking is a better way to deal with dipshits. I've seen guys that get counseling and put on 45/45 turn into bigger dipshits more often than guys that are smoked. Idk.

Whatever protocol is, that's what needs to be followed.

Would you be allowed to treat a civilian boss that way and keep your job? No, you wouldn't.

You signed a contract, honor it or gtfo

I would take the young man out and first , ask if he had a hearing problem. Then i would state that he would do the job or task and if he wanted to complain then we would address the issue once the mission is completed.

Drop kick that little puke in his temple