Why am I such a douchebag?

I'm a smart guy and I get good grades, I never skip classes essentially I'm very education oriented, I have lots of friends or at least people I can talk to and hang with. Any way people have been saying now for a while that I'm a douche to people or I'm mean person, but I do try to be nice to people I'm not out to get anyone, my mouth gets 3 steps ahea of me at times and I say something that I think is funny an no one else does they find it offensive, that doesn't happen often though. My friends say I'm a douche because I'm mean to others and act like I'm more intelligent than eeryone basically people think I'm cold and stuck up, I don't try to be it's just that my focus is generally fixated on getting good grades an not getting involved in the whole bullshit part of highschool, you know, who did what whose popular, I think maybe I'm more mature than people or something, idk I can't figure out why people think I'm a douche,