Well, FD doesn't see that as griefing.
Being a psycho murderer is a valid play style. Who knows, there could even be a motive behind it...a long time grudge with the Fuel Rats, perhaps.
Harassing players (killing them over and over, ultimately preventing them from playing the game, at all...also includes using game exploits to negatively affect other players) is what they consider griefing and it is not permitted.
NOTE: Not supporting or attacking a definition of griefing here. Just relaying my observation of FDs treatment of these situations.