Snitching isn't cool, but there are very few times when it should be done. The only time it should be done is when your life is in danger, or someone you know who's life is in danger, and by danger, I don't mean the bully is going to beat you up, I mean death, deadly danger.

Other than that, mind your own business. People get killed all the time for putting their nose in where it didn't belong, so it's best to stay out of other peoples business.