Yeah, most people on Xbox Live are douchebags or 12 year old kids, sadly. However, it's definitely worse in some games than in others. In Halo 3, for instance, people were really bad in my experience. Teamkilling, teabagging, cursing in the voice chat, quitters, I saw it almost every match. While in Team Fortress 2 (which I've been playing a lot lately), people are much more mature and willing to cooperate, and friendly even. I don't know what game(s) you played but maybe you should try some others.