One of our players is quite funny.He's said things that make everyone laugh. And his PC tried to play practical jokes on the dwarf. I didn't see that he crossed the line into griefing and I told both of them that if players wanted to have some kind of interparty conflict like a practical joke or gambling that the players could invent whatever rules and resolution techniques they wanted and the results only stood if all parties agreed.
Playing practical jokes on someone would be fine, locking the door behind you and trapping another PC alone with a pissed off troll is not.
It's not that the PCs can't disagree or even have different goals, it's just that those goals can't be completely irreconcilable. For example if Bob wants to protect the kingdom at all costs while Sue wants to bring it down, those goals are incompatible and eventually it's going to lead to PVP.
That may be perfectly OK in some games, it's just not something I want to deal with. Unless of course I can come up with some twist where Bob and Sue change their goals as new information becomes available.