I think a better statement might be, "if you look like you shouldn't be messed with, then they probably will leave you alone." My experience is that the ones that "look for a fight" usually get what they're looking for. There's always someone who thinks they're tougher and meaner than you are and is willing to stand up to that "I'm looking for a fight" game.If you look like you are ready for a fight they will leave you alone.
Just my 2¢ worth...