Dog stereotypes, do you fall for them?

I'm not really though I do have a bit of a dislike of "rat dogs" because most I meet are snappy, yappy little sods but I do know a few I like. My mum is very wary of german shepards and insists that they will all just turn on you because her nan had one when she was young and it just turned one day for no apparent reason and had to be fought off with a kitchen chair. I have tried to convince her that they arent all like that but its like talking to a brick wall.