There are not true at all. They are selective vehicles enabling prejudice.
All fat people are not jolly.
All minorities are not lazy.
All blondes are not dumb.
The way to think about this is to imagine that someone made certain assumptions about your character, your personality and your actions with absolutely no knowledge of you. Would that feel good to you?
@poofandmook Lots of people are prejudiced. That does not mean it is right.