You know, some people have incredible gaydar. They can instantly ascertain whether someone is gay. Me? I have incredible bitchdar. I always thought that Kristin Davis from SATC had that bitch aura, and I just read that, after she filmed her last scene, the crew sang "ding dong the witch is dead".
As someone who was taunted off and on as a child (don't cry, i still had friends), I can always tell if someone is or has been a major bitch.
My back goes up, my fists ball up, and I feel like the needle has gone off the record. No matter how sweet that person is being, I can tell they are out for blood.