FFXI said DD
All other mmo i have played call them DPS
DD = Damage Dealer
DPS = Damage per Second
"Hold on guys, I need to switch to my damage per second".
"Wait, the damage per second is not dealing enough damage, we need a new damage per second!"
Just because the acronym doesn't technically make sense isn't really important. How often have you heard someone talk about an "ATM Machine" or a "PIN Number?"
The word "toon" predates WoW by quite a bit. It goes all the way back to the beginning, when MMORPGs were called Graphical MUDs and the art was super cartoony because it was easier for the machines of the day to process. I realize it grates on some people because they don't want to think about the fact that their avatar (which is a far more correct term you will never convince anyone to use) is an animated figure on a screen.
Bottom line, the purpose of language is communication. If you know what they're talking about without any difficulty, then communication has happened and nothing further needs to be accomplished.