1) Bard that pull aggro then proceed to kite the mob -away- from the tank, then yell at me for not picking it back up
2) Lancers/monks/DRG that go all in on pull starts before I've locked aggro in
3) Tanks that aren't ready for BLM flare (or dreaded double flare [I announce mine for a reason])
4) WHM that keep recasting regen, even after I've removed it intentionally
4a) Also, let us not forget Cleric Stance.
5) Summoners that let their pets run wild/let them run into pulls
6) Pallys that forget Savage Blade -> Rage of Halone and just use Riot Blade/Flash
7) Scholars that let their fairies heal entire dungeons (doesn't work as well with WAR tank) so they can use Ruin.
8) WARs that ask "What's Provoke?"
9) BLM that doesn't know BLZ/FIRE 2 is not the best for single targets.

Did I get everyone? Moral of the story: Everything annoys me, and I feel like everyone should get some (yes, I play BLM, so sharin' the love :P )