"If someone called themselves a "Christian" or "Buddhist", but then did something obviously un-Christian, un-Buddhist, and un-nice, does it mean that Christianity or Buddhism are necessarily evil or un-nice?"

Giving a vague definition to some philosophy/ideology/methodology then claiming the good things that arise out are inherent in it while saying the bad things that come out of it are external. Classic. (Sorry, I can't for the life of me express this clearly. There was an article on Agile recently that said it better than I can).