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

I would react how every Sergeant (or E5 equivalent) should. Tell that PFC to stand by. Dismiss the unit to carry on with their days work. Order the PFC to stand at attention and ask obviously easy questions to help him understand he is not following lawful and direct orders. Ensure you are being as condescending as possible, due to the blatant disrespect for superiors assigning them a job. You need to correct it on the spot and ensure they are aware of the TRUE repercussions for disobeying orders.

From my experience in the Marine Corps I can't imagine this type of situation even happening.

Be a leader and pull him aside to address the actual issue as an individual. Or you can be like most of the 70’s boomers here and just claim you would publicly flog him after running 25 miles uphill in the snow both ways.

First of all, that is blatent insubordination and needs to be addressed immediately, appropriately and sternly so that this person's peers don't think they can get away with insubordination as well. When I was in service, this would have resulted in a quick trip to the First Shirt and Commander's offices and possibly an Article 15 at the very least; maybe a loss of grade as well.

I served with the 101st back in the very early 1960s. I was an FO for the 81s & a mortar squad leader. (Buck E-5) I kept an extra blouse with no stripes on it for such occasions. I rarely had to use it but it was for those rare times when after hour’s instruction was called for in the event someone had a problem with my leadership abilities. Such things were not allowed officially in those days but they happened. These days with political correctness and all, I doubt such advice would have any bearing on anything. Like all older folks, we naturally think our days were better. ABATW.

It's 6:45 AM, Vegas Time~ Monday, ~ 02/13/2023~
And I've Been MOSTLY Just Reading These Posts,
For About TWO HOURS Now....
GENTLEMEN.!!.....When I Read YOUR Comments,
And Your REPLIES
You MEN Make ME Proud,
Just To Be Here With You !!
THANKS,
The Gods Know I Love Ya !
RICK

Have the E2 report to my office put him doing 50 good pushup's when done ask wait is your complaint with the job. At that point hand him a shovel an tell him all the sand on top to one side so the ground can be tested or get a AR15 faster than his or her moth can move you are the NCO not them.

A good old fashioned fan room counseling session worked back in the '80s.

Bring them up on charges

Not get on here and bitch about it. Clearly this E-2 knows they can punk you, and what the hell is your MOS. The cook? Interior designs? Hopefully you and that E-2 are no where near any combat related job