Initial enmity generation and player bad habits.

[Ignnis]

Tank just used lob and is herding everything to flash and scorn but the amazing blm decides "fk it" *SWIFT CAST + FLARE BEFORE FLASH* Whyyyyyy!?!

The other amazing things that have graced my retinas during dungeons:

Auto fairy pulling bosses.
DPS that like to pull.
DPS that don't know what marks mean.
"No healing or dps before the room glows while on ultima" *tank runs to pull ultima, tank just about to use lob, WHM casts regen, Ultima ping pong match commence.
WHM that thinks medica II must be kept on at all times.
That cleric stance healer.
Tanks that use sword oath to tank and refuse to swap to shield oath.
Tanks that think they're DPS and spin monsters to attack their behind much to the melee DPS's annoyance.
Tanks pulling with provoke.
"Tank just pulled quick unleash the AOES!!"
Lets pull the boss before the WHM has the chance to get MP back.

Personally sometimes I accidentally refresh regen on the tank when the last monster in the pull is about to die then the tank goes to pull more and everything starts nibbling my legs, reflex sadly, I just auto pilot regen -> CS -> DPS mode. I deserve those nibbled legs...