A man, who's been holding down his spot at the bar for quite some time, beckons to the bartender and manages to slur out, "H-hey man... I need to use your toilet before I go."
Barkeep nods, and points to the staircase in the back of the room.
"Up those, first door on your left."
The drunk manages to stumble his way up, much to the bemusement of the other patrons. Barkeep thinks nothing of it, until about 5 minutes later, there is a blood-curdling scream that lasts a full 10 seconds before a hushed silence falls over the bar. The barkeep quickly assures the patrons that the drunk man is fine, he's alone, he's just being stupid up there, somehow.
5 more minutes pass before a tortured wail of pain echoes once more from the stairs, and now people are beginning to leave. The barkeep, not wanting to lose more business, leaps from behind the counter, sprints up the stairs, and swings the door open to reveal...
The drunk, sitting down with his pants 'round his ankles. The bartender, furious, begins to shout,
"You drunken dumbass, what are you doing?!"
The drunk shouts back, in a mixture of pain and rage,
"Hey screw you, man, every time I flush your damn toilet, it bites me!"
The bartender shakes his hand and points to the porcelain throne in question.
"THAT'S my toilet! You're sitting on my mop wringer!"