So I've been playing a ton of tf2 lately and I've noticed normally hatful players in tf2 normally take a relaxed approach to the game and mess around with players on the other team while they could easily be killing each other. This video being a good example.
http://www.youtube.com/watch?v=GoFgGimHnyY
I wondered back to wow, have you ever seen alliance and horde players who don't know each other being friendly when they could be killing each other? It doesn't seem like something that happens nearly as often.