My friends' parents seem arrogant?

Okay, I know I'm not supposed to judge people, but seriously, my friends' parents aren't just seemed arrogant, but they act arrogantly. I dunno if this has something to do with wealth or something, but my friends are very rich and I'm on a snobbish school but I'm just a typical, I live in suburban areas. Sometimes, when I walk with my friends, their parents would come to fetch them, and I would look at their parents and smile or wave, but they would give me a cold stare as if I owe them some beers. They really stare at me like I did something bad to their kids. One day, my friend gave my friend and me a ride but his parents seemed uneasy. I wasn't smelly or dirty and plus, I was behaving politely. They didn't talk much to me, but they talked a lot with my other friend, which kinda made me feel left out. I'm kinda talkative and friendly, but they make me feel so awkward to talk to them. Then when I start talking to my friends, they keep making cough sounds so hard. I don't know what's their problem, but what should I do? And why are they acting like this with me? I really hate it. =(