Only time I would ever rage quit was as a tank when some nub would pull aggro all the time off me, even after repeatedly telling them to back off at first and not go nuke crazy right at the beginning.
I've let many a mage/lock die from pulling stupid shit like that. It's always the best when you let them die, the healer doesn't heal and when the dps asks "wtf" the healer has my back and says "Don't pull aggro and you won't die". Lmao