Well, of course there's murder, rape, etc, and obviously those are bad.
But, I think what's worse is not even really a crime - at least not on the book of adulthood. It's the stuff that is "not tolerated" in school yards and the classroom. It still happens though, and is very hard to prove or see.
It's bullying, teasing, putting others down to make yourself feel better. In the adult world, it takes the form of talking behind someone's back, CCing people on emails that don't need to be in the conversation, going out of your way to make that person miserable.
Don't get me wrong - I've been on both sides of this. I know I've done my share of making other's lives miserable - as ashamed as I am to admit, as an adult and not just the kiddie version. I've done it when I know better. Here's hoping I've learned, but the truth is, we all have these moments where we do it.
I do think though, for the betterment of humanity, we just need to try and be nicer to everyone.