I do.... when their age becomes obvious to me. It's not that I hate the younger generation(because I can acknowledge that I was once there!), I just can't stand the teen gamer personality. (they all act like that friend you have.... you know the one, the one with the kid brother who thinks he's all that and bag of chips)
...it bleeds into the actual game like a plague and infects every server.
Even when I used to play online games on my PS2 and gamecube as a teen I hated gamers my age because they were asses.