Think of it like a dinner party. For the most part, people put up with oafishness. Get out of control, and people will either ask you to relax, or show you the door. No rules needed. Mostly, adults know how to interact with one another, and can generally tell when they've gone too far.
If you think other things went too far, and are surprised in this case, just be aware that everyone here is human, and doing it for fun. If you'd like to pm someone about a thread that's out of hand, feel free. You may get some grief about it, or it may get locked. Heck, if it's bad enough, we may even send you their home address so you can go solve the problem in person.