Personally I think you wait till he is in a large group with his peers and say something to the effect."Hey your that idiot that told me ..."and finish up with "well assneck sort your shit out." His peers will proably laugh at him as if he is shooting this bull at young guys, he proably is known to be an idiot by his peers.Maybe you get charged,maybe not.But hey you'll be remembered as they guy who told Cpl soandso he was a idiot and sorted him out.And then mcpl......anyway.
The army is a really weird highschool,his friends will hate you (later messing with your career...it happens)but the other guys who thinks he is a assneck will love you forever.
Everyone kinda knows myself and being reserved and quiet.....nahhh they dont.