What anime is this?? It's bugging the crap out of me.?

I saw it on adult swim. The teme opening had all these characters like floating around and laughing but the song was kind of catchy. There was this guy in roller blades that killed people or beat them up with a hockey stick but I never saw his face fully. In the episode I saw these two kids were running for class president, a fat and skinny kid. The skinny kid is all popular but when the fat kid starts getting more liked and could become class president he gets beat up(maybe killed) by the guy in roller skates and everyone blames the skinny kid and thinks he did it. Anyone know??