YouTube seems to be the viewing of choice for the younger generation. My kids (21 & 17) rarely watch tv, but will spend hour after hour watching videos on YouTube given the chance, and the more puerile the better as far as I can tell. The ability to add "witty" comments is a bonus.
For a lot of people it seems to be that if you can't become famous, you can at least become notorious through trolling. YouTube comments and Twitter appear to be the main vehicles. As has been said, it's the online (and therefore much more public) equivalent of mindful vandalism. It's a sad part of human nature, so it would seem