The last few times I played TF2 I was really disappointed in the other gamers.
But the biggest disappointment so far was in how the Mechwarrior online gaming culture changed when the closed beta ended. Before people had been civil and friendly, once it opened up... Well, the civility lowered considerably.
One time, I greeted the other players and wished them good luck as it had been customary for everyone to do and the replies were insults at me and demands that I should quit the game.
Also griefers appeared around that time... I just can't stand griefers.