1. You join a session, idle. They kill you, then leave and you never see them again.
2. You place a $1,000 bounty on a griefer just to make him an easy target for yourself and others. He hides in his apartment. WITH A $1,000 bounty. This is enjoyable to see, however.
3. You're riding a bicycle in passive mode. A user shoots and kills you.
4. A user continuously griefs others while in a tank. Tank gets blown up. He immediately runs away and gets another tank. Makes no attempt to fight outside of tank.
5. Player in tank realizes there is sniper trying to kill him. Hides in alley, doesn't move. This too, is actually funny and enjoyable.
6. You intentionally go after somebody with a high K/DR who is abusing low level players. You kill that person once or twice. He runs away, stops killing people, or leaves the session.
7. Using God mode.
8. Running over somebody and running away, never to be seen again.
9. A high level player exiting a mission because low level players are in it.
10. Repeatedly griefing low level players with inferior weapons session after session.
I notice this all the time when using my recently created 2nd character. High level bums will hunt me down. Another reason why K/DR doesn't mean much in this game unless the player actually goes up against good players often.