Squats (real heavy squats, none of this bar & 2 10lb weights bullshit) develop your quads, so if you want your butt to grow your legs will grow too leaving you with not skinny legs (lean and muscular, yes).  Personally I hate being called 'skinny', I bust my ass in the gym 7 days a week to not be skinny. I'm lean. I'm muscular. I'm not skinny.  Plus fats hate it when you tell them you're not skinny. ;) *When I think skinny legs, I think like this as opposed to not skinny