People who just can't shut up
Irritate me to no end. What's the use of saying out loud every single thought that passes through your mind, even if it's meaningless? And I mean friendly chatter mainly. Once I had to leave a common PC room, because a guy with an unpleasant voice kept on speaking to his friends in a loud and monotonus tone that I just couldn't stand for long. An other time I left an online game because they went on chatting and laughing about absolutely NOTHING noteworthy pretty much without a break, and I thought could well continue for hours.
But I'm sure it's all completely normal, what was I thinking, fun just isn't for me, they will never speak to me again. Ah well.