"The answer to 'When does 'RP' become griefing?' is simple: It's the moment when a person exploits the nature of the game (and ignores the spirit of role-play) to detract consistently from other players' fun. On the flip side, the spirit of RP is not to always win, so if you can't lose sometimes and still have fun, you're also violating the spirit of the game."
"So, if your argument is, 'I'm RPing', and being a total dick. Goblinworks should happily reply with, 'Okay, we're RPing Pharasma and she just revoked your resurrection priveleges' (this is an actual concept within the game's RP). Then they kill you and boot you, and they 'RPed' it."