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

Write him/her up for office hours, needs to realize who is in charge. Semper Fi

Would see the troop with his supervisor after formation, remind the E3 there is only 2 ways he is allowed to address an NCO, Parade Rest or Front Leaning Rest their choice but they better pick one right away. Explain to his supervisor that he needs to get his troop in line and back up to standards or I will and I promise he wont like the way I will. IE recommend Article 15 for insubordination etc. Look the troop dead in the eye. Which means you may have to get in the front leaning rest with him or her and remind them that they are acting like a "soup sandwich" and if they want to stay in your military better get their head out of their 3 points of contact and fall in line like the others or better yet you don't like working/taking orders from me then you best get promoted and promoted quick because I guarantee you wont see any promotion on this road your on! Your choice! Then let his supervisor handle it via verbal or written counseling. The supervisor should know his troop better than you, not an excuse for you to not know your troops however, and he will get said troop in line or that supervisor will not be one for long.

Finish giving out tasks for the rest of the formation. Dismiss the formation and have the pvt stand by. After the rest of the formation leaves the area, discuss the lack of respect not only for you but the rest of the platoon. Explain how his insubordination tears down cohesion within the unit and won't be tolerated. Tell him the tasks assigned to him are just as important to the mission as your tasks are , and they are within his current skill set. Explain to them if the behavior persists, you will recommend other punishment under UCMJ.

Corrective training. He would now be required to give a class on military courtesy and rank of not less than 50 minutes to be presented to the whole company at the next training day. Said program would be reviewed by me and the upper echelon of the unit for accuracy and completeness. This class would be prepared during the next weekend since he will be restricted to barracks for that period.

You must nip that in the bud very quickly,
I would have ordered the member to stand outside of the chief Mess,( E-7 AND ABOVE) the Junior Member Will be order to stand at the Position of attention every day for the next MO, outside of the Chief Mess, until he is called in, for a Uniform Inspection, this will happen Monday - Sunday, every day right after breakfast.
Once Member has completed his uniform inspection, the Senior Military member will inspect his living quarters, after that is completed, he will be given every shit detail we have.
on top of that, Member will be given training to his fellow service member on custom & Courtesy, on How to wear your uniform correctly, what is and is not a lawful order. etc.
it is the job of the senior Enlisted to ensure the junior members have pride in there military service & Uniform.

I have found when I have a smartass member, or a Member who does not have pride in his service and work, the member does not have pride in his Military service, does not have Pride in his uniform Appearance or in the work he or she is assigned to complete most importantly he or she does not have pride in themselves , it are job to instill that pride , and to mentor junior member

My point is, those who do not have pride in there uniform do not have pride in there service, or pride in there Work, once member starts having pride in his service and uniform he or she will have pride in every job he or she is assigned to complete. it is amazing how that works .

I would release all others and give him a second chance.If that does not work ,I would escort him to first Sargent and explain the situation in front of first Sargent and leave it to first Sargent to dish out punishment.

Gunny Pepper is absolutely correct. The PFC and his supervisor must be called out immediately. The correction must be made on the spot without hesitation or reservation. In my 33-year career, I have had the pleasure of serving with the Marines on numerous occasions both in Peace and in War. Never had a problem with any of my Marines in following my ORDERS. RICHARD L. MILLER, Lt Col, USAF (Ret)

Ordinarily counseling someone should be done in private. However, in my opinion this incident is an exception to the rule. This was a blatant act of disobedience that was done in PUBLIC. To not respond in immediate time, allows other individuals within the unit to think this young joker just got away with something. Let the punishment fit the crime, mouth off in public, expect to hear about it in public.

I would wait until all are dismissed except for him, then march to the orderly room and 1st Sgt to discuss punishment. Needs to be put in his place now or he will be a problem from then on.

After formation find out what’s really going on with the troop. If it continues then counseling and or UCMJ.