Most likely the former, I think. An ego thing. Sour grapes. The same as men who are turned down by the ladies declaring they must be lesbians. I've also seen people grunge their looks (sloppy clothes, unkempt hair, no makeup) in order to blame that which they can control, their outward appearance, for being rejected instead of themselves and their sucky personality, which they can't control.
I must confess that I stood up the absolute nicest, most generous person in the school, the kindest I have ever known, out sheer immature selfishness, and that act will haunt me to my dying day. Sometimes retaliation is deserved, if not for the reason given.