Annoying little things.

• People that don't put a buyout on consumables/trade goods on the AH. If I'm levelling leatherworking and need 3 Black pearls to do so, I'm not going to wait for 24 hours for your auction to finish because you're too stupid to put a buyout on your auction in the hope that bidding on your pearls will go through the roof. I'm going to pay a higher price to get them now! Stupid people.
• Beggars - Some clown in Org today said "Can I borrow 69g, I want to buy a Fiery War Axe" (which incidentally is an an overpriced piece of crap anyway). I laughed at him and told him no. He argued with me when I said it was crap and not worth the money he wanted to borrow from me to buy it. So I said "ok, you tell me what makes that such a good weapon". *tumbleweeds*
• Passengers - people who want the purple loot and the thrill of seeing end game content, but are too lazy and/or stupid to gear/skill themselves appropriately.
• Extended maintenance when there's not a patch. Actually *ponder* extended maintenance, period.

The list is much longer than this, but I can't be bothered at the moment :)