My little brother is a bum what should I do to help him?

Sorry this is long. I love him very much although hes annoying at times he's my best friend in a way and knows me/understands me better than anybody including my other best buds. The problem I have with him is he barely has concern for his looks whatsoever. Now I understand we're guys and should not be over-concerend with looks at and trying to perfect ourselves or whatever; that I get. But you should still have some pride in how you look out in public when your going somewhere. We were going to Dave and Busters and he thought he was just going to walk out in just an old school Shirt and basketball shorts. Anywhere in the house and playing outside is fine but not to Dave and Busters. How should I tell him that? How can I tell him to spend at least a little of his money on a decent shirt on sale instead of a new video game!? I wouldn't have a problem with it normally but its just at the point where sometimes I find myself having to let him borrow some of my shirts. (hollister fits a little small plus hes not much smaller than me {we're 11 months apart btw} so he can get away with it just fine) My parents have bought him lots of nice shirts for him to wear FOR SCHOOL next year he cant touch them yet. When me and my mom go to the mall he never wants to come which makes me SICK because he expects us to get him something wedon'tt know what he wants! My mom alwaysvolunteerss to buy him stuff (I have to pay for mine which is fine) but we never know what he wants+he never comes sothat'ss all his fault. I know he wont be a bum at school he'll be fresh and all but now during the summer I want him to be fresh too how can I convince him to buy a nice little shirt to go out in every once in a while. I think hes realized that he has nothing to wear and as a resultdoesn'tt want to go anywhere. Usually he'll be down for anything. Should I just have a private conversation with him man to man big brother to little brother? I have on several occasions volunteered to buy stuff for him but my parents dont allow that; they want him to use his money on him which is fine by me. So should I have a little chat with him? What should I say? Any other advice? Thanks!