Piss in the Boat
Two men were out fishing, when they found a lamp floating in the water. One of the men picked it up and rubbed it, causing a genie to explode from the lamp. Unfortunately, it was a very low-level genie and could only grant one wish. The men thought for a few minutes and then wished for the entire lake to be made of the best beer in the world. With a poof! the wish was granted. All of a sudden, one of the men got really angry.
"Dammit! Now we have to piss in the boat!"