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

Had a similar incident happen as a 1SG. One of my PSG’s passed assignments to Sqd Ltd E5, who in turn gave the assignments to Sqd members. One PFC was obviously having a bad day. Turns out he was totally insubordinate and was brought to my office. Turns out he’d been diagnosed with HIV. The insubordination was his reaction and acting out. He was immediately referred to our assigned PA, to begin a process of counseling, medical assessment and treatment. Assignments were altered to accommodate his new Chronic medical condition. He’s non-deployable and like many autoimmune patients had a dramatic increase in sick call attendance. Soldiers are our most important resource. Caring for them requires, as leaders, acute attention to details. Discipline is only considered after, all facts are investigated.

Having been in that situation many years ago, it was: "Beg your pardon, I am a bit hard of hearing" followed by "Okay, not a problem, stand fast after I dismiss everyone" After everyone else is dismissed we go into the shop office where our CW4 Platoon Leader dwelled and said Private repeated what he said in response to my order. Chief asked if the door to the office was locked and I affirmed that it was. And what followed was one of the most spectacular non-physical, low voice volume ass chewings that I had and still have ever seen and heard that was a combination of remedial physical fitness training and detailed explanation as to the error of the ways of said Private and a caution that if the situation repeats itself said Private's military service, if not ended, they would be hard pressed to see additional rank. The Private in question came away with a better understanding of what to say and what not to say when an NCO gives them an order. Said Private, by the way, became a Warrant Officer later on and retired as a CW4 themselves. I came away with a lesson learned that one doesn't always have to be loud, forceful or resort to killing trees to correct an individual in helping them to see the error of their ways.

i would insrtuct him to report to the company commanders office at 1300hrs and have the company clerk to draw up paperwork for ucmj action disobeying a lawfuull order of an nco and derilection of duty, afterwareds i wpuld hold a mandatory meeting with my platoon to let them know this shit isnt going to slide, We work as a team and that means ladi doti and everybody

I'm sure reading a lot of 'touchy-feely' bullshit from you newer Vets.
GySgt. Pepper had it technically correct, PO1 Gibbens had it physically correct. Nobody wants to do the crap jobs, but when you're E-1 to E-3, guess what? That's your jam! It's the dance you do. Don't like it? Gain rank or GTFO. Before securing the formation, I'd choose my senior E-3 (The most terminal rank 'Grand Old L/Cpl Of The Marine Corps' salty fuck in the unit and order him to go do it in PFC Shitbirds place... PFC gonna learn after 16:30!

If I out rank them I will tell them one more time then if they tell me to stick it again I will with the plt. sgt and the plt. ldr write them up if I am the plt. sgt I will process them for article 15's.

there may be an underlying issue higher command is seeing you are not? An order is an order, you really don't have a choice and this is the time to try and decipher their reason of logic. Maybe your being tested?

I’d explain to him what an Article 15 will do to his career. I would also restrict him to the base for a short period of time.

When I Went into the Marine Corps If You were that stupid try to give an answer like that you would very quickly find yourself picking yourself up off the ground and still do what you were ordered to do. Y would not even think about trying that ever again.

'59 to '79, when I was in, it would've out of sight and taught the error of his ways!!

Keep the Pvt and his team leader after formation, explain how the army works, afterwards write a formal counseling statement. And introduce the young man to the school of the soldier on the weekend/weekends...take his time and continue until his behavior changes...I see no reason to take this fwd to ucmj at this point. Inform psg of the corrective traing plan and carry on.