Why are some people so easy to pick on?

I’m not talking about the grossly overweight star wars dork in high school, or that guy in your group of friends who always manages to say exactly the wrong thing. I’m not even talking about the really short guy or the really timid girl. Some people, as I’m sure you’ve noticed, seem to invite dismissal and ridicule from their friends and sometimes even from strangers. These are perfectly normal people, perfectly likable and for the most part well-adjusted. Nevertheless, they possess a certain je ne sais quois that makes them a target for insult. Can you explain why this is?