On V:tM: Yup, turns out those rules about not touching are there for a reason. Can't count the number of times someone touching someone else appropriately caused problems in live RP. Unfortunately, none of them were game breaking in my xp, so I can't share there.
As for everything else, where do I begin?
The first player who broke one of my games was a stickler for detail. At first, rather harmless detail, like what he had for breakfast or choosing a vintage of wine. Had the most detailed character description I'd ever seen that took up ten pages alone. THEN the problems start. Casually asking the DM what the time of day is and, upon discovering that it was morning, informs us all that his character (a woman, though he was a man... nothing unusual there, though) is going to the toilet. He then proceeds to describe the act of going to the toilet in excrutiating detail based on the contents of his meal 8 hours previous. I'll spare you the details, but she was on a high fiber diet.
Ok, we're all getting freaked and the DM's moving us on and we're trying to ignore this crazy dude. We think he gets the hints we're dropping like great boulders every time he starts up (amazingly, toilet activities are the ONLY thing this guy describes in full detail). Then, we camp for the night. And this guy says that his character is going to stay up and masturbate, loudly. I don't know whether he was pissed off that we wouldn't listen to his scatology or if it was just another of his perversions but several of the players got up and left and we kicked this dude out of the house so fast it took a moment for his eyes to follow.
We were so traumatized that we didn't play for a few months before starting up again from scratch.
I'll also remember unfondly the day I played with a bunch of college acquaintances. Please note: this was an all-male party. We're palying along, everything's going ok, then the male dwarf fighter gets killed by a lightning bolt. It was from a Behir, I remember that distinctly and you'll know why soon. So the encounter ends and I tell the DM I'm searching the area for loot, as you do. One of these guys gets a thoughtful look in his eye and says to the DM: "I rape the dead dwarf."
Maybe I have a more highly developed imagination than most people, but the image sent chills down my spine. The dwarf's player is coughing and spluttering but he's dead and can't to a thing. Whether to annoy the dwarf's player or whatever, the rest of the group quickly takes up the cry of 'Rape the Dead Dwarf' and soon it turns into a gang rape. Sickened, I get up and tell everyone I've got to go. As I was leaving, I heard cries of 'Rape the Dead Behir'.
The poor DM... it was his house, so he couldn't leave but he refused to DM with them after that.
So, in-game shinannigans killed another campaign I ran, this time in Shadowrun. Picture the scene: The runners need to break into an ultra-secret research facility outside Seattle. It's fairly small on the surface, fenced off except for the gate, and I clearly describe to them the guard tower that overlooks the entire compound. Their solution to infiltrating the site: drive up to the front gate in their ordinary street car and cap the guard at the gate. Note that the gun they used was not silenced.
So there they are, the guard bleeding to death on the sidewalk next to their car and BLAM! A sniper shot takes off one of the side mirrors. One of the players panics and says "I open the car door and drag the body of the guard into the car!" Don't ask me what this was supposed to solve. The rigger's player takes exception to this, however, saying "No you're not, you're not getting blood on the interior of this car!" The other guy says to me "I pull him in anyway." The rigger's player says "I reach over the back of my seat and physically restain him!" I pointedly ask what the third player is doing and he just shrugs, so I'm on my own.
Blam! The sniper (think he's shooting from the guard tower? Yup, you guessed right) puts a bullet through the engine block. The players realize this but none of them seem overly concerned that someone's shooting at them or that their car is disabled. The rigger and the guy in the back seat get into a proper wrestling match while the third just sits their doing nothing. Finally getting sick of it I just said "Ok, the third shot goes through the gas tank, the car explodes and you're all dead."
That was the last game of Shadowrun I played with that group. Somehow, they all agreed that yes, they knew they were being shot at. Yes, they knew that the car was disabled and they agree that the blood stains on the interior would have been a minor problem compared to a bullet going through the engine. And the character who did nothing agrees that he probably should have done something, even if it was just running away. But somehow, I'm a killer DM...
Go figure.