My son is at the age where he's really starting to feel himself

Last week at Penney's when we were buying him shorts he found a sleeveless slinky adidas shirt he wanted me to buy him. I'm all for him expressing himself as long as he doesn't embarrass me in the process so I was game for buying him the shirt. But he picked up a size small...and he was serious. There was no way on earth I was going to let him walk out of that store with that tight ass t-shirt so, luckily, his annoying ass dad talked him out of it over the phone and ended our arguing. He sulked a bit but got over it.
Fast forward to Saturday and we're perusing Marshall's. He comes over to me in the dress section with two Under Armour brand shirts, visibly excited. Rats, I think. He see's my apprehension and tells me that he's just interested in working out in them. And since they're relatively cheap I agree to buy them on the condition that they fit. So off to the Fitting Room we went. The black one was flattering, the white one was snug and I could see his nipples through it. Not cute. But he swears he's working out in our garage in this shit so I don't challenge it. How about just today he tried wearing that white tiddy top shirt to the dentist!? He comes traipsing into the living room in some cargo shorts, that super smedium sexy white shirt, and a hat cocked to the side looking like a zip damn fool. I just glared at him and said no. My mother wants me to encourage his freedom of expression which would be fine if he weren't out with me in public. And even if he isn't with me he looks just like me so everyone will know he's mines. I am not about to allow him to embarrass me like that. I may have to hide that white shirt. Or destroy it.