I used to assume that the really fit girls at school acted so stuck up because they knew full well just how fit they were, and they wanted to lord it over me and my friends just how little of a chance we had with them.
I also used to assume that the guys who acted the toughest were doing so because they actually were the toughest, and that they were doing us a favour by letting us know just how little sense there was in challenging their authority.
My Wizard of Oz moment took years, sure, but eventually I realised how full of shit they all were. The fit girls were just girls, petrified of being seen as mingers. The tough guys were just guys, petrified of being seen as bummers.
Look beyond your first impressions of people. Especially the ones who intimidate you. They are often the weakest of all.