I'm being this person right now. FFXI is blowing my poor little former-WoW-playing mind. I'll probably continue to use some of the ones that aren't game specific (obviously "taunt" and "voke" need to stick to their respective games) but eh.
Personally, I have to keep up the FFXIclopedia dictionary when I'm playing. Seriously guys, do you really have to shorten party to pt? SRSLY?
As far as strange WoW lingo goes, the most confusing has to be place names (BRD vs BFD, ULDA vs UBRS vs LBRS, RFD vs RFK) not to mention all the VC vs DM debates (and DM will always stand for Dire Maul, noobs). I did get confused with omw. I think that was it for any slang one could actually use for anywhere that isn't Azeroth.
I did once say "Come on guys, let's hearth" in real life, that got me some odd looks.
I do have to say, the best thing about game lingo is once I start talking with someone who plays the same MMO, we can successfully alienate anyone else from the conversation in a way almost nothing else but speaking another language can.