Abuse is never warranted, if someone isnt performing you can tell them without being rude.
Last night, I had a player who just very recently returned, we were doing the Great Library of Gubal and the tank pulled about the whole dungeon up to the first boss, he died blamed the healer and then left. Healer asked if he was that bad, I responded no, some people just cant STAND the dungeon taking 3 minutes more than usual, we got a new tank and it was a smooth run from then on. Point is, theres absolutely no reason to be an ***.