I disagree with Superhunky a bit on that one. While for the most part, he has some fairly solid rules of thumb, I think he's taking that too far. I have come in contact with enough people with weird things going on to know that not all of them are assholes. Many of them are, sure, but that's not always the case. One of the nicest people I know went around for two years with a gnarly set of dreads, and he's blond-haired and blue-eyed!
And on the sticker thing, that really depends on your own viewpoint, which is and important reminder that another person's assholery is entirely dependent on who's being asked. Everyone has friends and enemies, right? QED.
And one last thing. He also says you can't tell by the year, make, or model of their car. Bullshit. Toyota Prius. End of Story.