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

Squash him like a bug and PT till he pukes. Questioning with discretion is one thing, in formation. Very wrong answer.

not much you can do in todays military. in the old days i would kick his ass to send a message to the other troops! i am in charge and you maggots are gonna do what i tell you to do when i tell you do it it-or else!!

I actually had a situation similar to this happen. I had assigned a group of students to clean up our radar huts. I went and checked their work and it was substandard. I then went to the class room gathered the students up and we headed for the radar huts so that I could supervise them. A LCPL decided to tell the others how those God D@#m SSGT's think they own the Blank Blanking world. He did so in my hearing. Once he peeled himself off the wall we continued to the radar huts where they spent the rest of teh day cleaning, and cleaning and cleaning.

I would probably tell him to report to the First Sgt. and tell him that. Has Ha

Lock him up, put him at ease...initiate immediate Counseling Statement for his file at very least. Depending on the severity of his tone...submit request for Article 15 recommending reduction to E1, to include a fully written explanation to the Chain Of Command.

Tell he to report to 1st Sgt for Article 15.

I assume in modern times, it's probably no longer ok to punish everyone and ask the platoon to "help" him obey orders.
(By the way, what are those yellow straps they are wearing in the picture?)

Granted I am only up to Spc-4. However, if given a chance, I will make him stand fast after formation and explain himself. Smoking him outright will make it worse. However, if he is still insubordinate towards you, you gave him a chance and he blew it, then you can smoke the living hell out of him until he learns to respect. At the end of the day, at least you can say you gave him a chance to explain on why he's being insubordinate towards you.

Being in a unit (or formation) is like a well-oiled machine. Everyone has to do their part. If there is a problem, then that problem needs to be investigated so a possible solution can be made (within regulation). I've been told to disseminate to my subordinates (yes, I had a few privates that my SGT gave me to look after) any info/tasks needed to be done by the chain of command that I never had a problem in doing so. Leadership is all about keeping your cool, but being firm.

Wall to wall counseling.

Tell E2 and his first line supe to stand fast after formation. Allow him to speak his mind, and then discipline accordingly.