if they are mean to other people and animals if they lie/manipulate people if they are conceited say/do hurtful things/commit violent crimes(bullying,rape,murder,etc)
If they are stuck up. If they are bully others. If they are racist and prejudice. If they are homophobic. There are lots of reasons but those are kind of the big ones.
When they keep on bugging me. When we're talking and I listen to everything they say but they seem to forget everything I say. When they think they're always right but they're actually one of the biggest idiots in the world