I think a lot of people care what others think. One support for this argument would be that most women/girls follow fashion trends because they want to be perceived as hip/fashionable/good-looking—hence, they care what someone thinks about them.
I think everyone has someone whose opinion matters to them—for some, it is their peer group; for others, family.
Perhaps most of us who claim not to care what “people” think are the ones who don’t care what their peers think—after all, it’s different if a fellow co-worker or student doesn’t think you’re smart, but if someone who isn’t your peer, perhaps a professor or younger sibling thinks this, that’s completely different.
Wow, I wax philosophical late at night.