Why do people always think I'm stuck up?

I don't understand. Even in high school, many people didn't hang around me because they seemed to think I thought I was better than them. At work (I'm a waitress) the buss boys told my friend "Oh we think she's hot and we want to **** her but she's a stuck up *****" like wtf?! I always joke around with them and sometimes tease them, but I don't mean it to be condescending. Maybe I shouldn't think much of it, because I don't think I'm this way, but I can't seem to figure out WHY people think this about me without KNOWING me at all. I do like nice things and having nice things and dressing and looking nice all the time. But if I buy something expensive, it's because I pay for it, not my parents. I don't flaunt it around either. I'm always generous and lend people some if they need it. I don't understand.