What do you do when a soldier refuses to listen to your directions?

Ask again. If he still refuses; put him/her on report.

when did this man's force become a democracy ? :D

My recommendation to any NCO is to document. Nothing is worth getting emotional about. The pen is mightier than the sword. If you dont document then you might as well be quiet because being making a whole bunch of noise cussing and fussing will definitely be amusing to those watching but to the Soldier he's just waiting for you to cool down waiting for the next opportunity to break an Army regulation. You will be known as the weak NCO allowing your Soldiers to do whatever they want. Then your going to PCS and that Soldier will be someone else's problem! No such thing as likership, only leadership! Lead or get outta the way!

Write a counseling statement and give a corrective action that relates to the incident. Allow the corrective action to take away their time; for example if they show up in a messed up uniform or wrong uniform, during the weekend or time off have them report to the Staff Duty desk or somewhere every few hours in a different uniform and ensure you told them it has to be worn to standard. If, after that they do not listen you may have to recommend them for an Article 15. I hope it does not come to that, but sometimes when they do want they want to do, you have to do what you need to do.

As much as beating his face in would be lovely, I feel JAG frowns upon this.

I would definitely formally counsel him and make him do some sort of public remedial training (like forcing him to teach a company level block of instruction on AR670-1 or such). If he wants to be wild I’ll after that I would definitely push for NJP.

I will assume that the Army has a little thing call "disobedience of a lawful order". Stand him up before "The Man". You are building warriors, not wimps.

I would dismiss that Pvt from formation. Have him stand in the back of the formation until such time as to the end of the formation. Does he have a medical chit that requires him to wear them? I do know that soldiers that have corrective eyewear can get a pair of sunglasses as well. They are no stylist in any way. If he has a medical chit for them, then he/she is out of uniform as well as disobeying an order. He/she also has muttered under there breathe ( come on, we’ve all done that) which is another charge as well. I would not physically try to remove the sunglasses because that can open up another whole can of worms and you do not want to lose your professionalism or your bearing in front of other troops. I would write this person up and recommend UCMJ actions.

Article 92—Failure To Obey Order

First I'd give him one last chance. I'd take the glasses, toss them behind me, and then get in his face and speak these words: "I'm not giving you a choice. You never had that option when you signed that dotted line. Follow orders." If they still are beligerent, yeah, I'm writing them up and letting them feel the full brunt of the UCMJ. During the whole time, I'll also drive the point home how they're in the military and they are property, not people. If that makes them sad, we got therapists they can go see about it. Until then, they are expected to follow orders, but if they intend to keep flaunting orders, they can do so inside a jail cell.
Works every time!

Years ago SGT would of crushed glasses into his sorry head now adays it is not PC to touch your troops. Maybe a time out would be needed