I think you got "ganking" and "griefing" mixed up, there...
That being said, I've done this before, back in Wintergrasp. I play on a PvE server, so there aren't as many chances for it, but yeah... if you're standing there and fishing, and I'm feeling like screwing around, I'll drop on your ass and try to kill you. If you're a caster, you should be able to blow me away without your staff, or switch weapons. If you're melee, switch weapons.
Edit: Mis-read. They're wearing full Heroic raiding gear? That's their own problem, then. Too damned bad.