You've probably heard this one, but speaking of monkey jokes -

A man came into a bar with a monkey. The bartender told him that no animals were allowed in the bar, but the man assured him that the monkey was very well behaved and said he'd make sure it didn't bother anyone.

Everything was fine for an hour or so - until the man had to go to the restroom. Left by itself, the monkey went berserk. It ran down the bar knocking beers over, and everybody was trying to stop it. The monkey jumped on a pool table and ruined a game by knocking the balls around. Just as it was about to get caught, the monkey grabbed the cue ball and swallowed it. The man came out of the restroom, and the bartender threw him and his monkey out and told them to never come back.

A year later, the same man came in to the bar with his monkey. The bartender remembered them from the year before, and told the man they couldn't stay. The man assured the bartender that he'd watch the monkey better and that it would be OK this time.

Everything was fine for an hour or so, until the man went to the restroom. Left by itself, the monkey went berserk again. It ran down the bar knocking beers over, and it started eating from the bowl of free peanuts. The monkey would take a peanut, hold it up and look at it, stick the peanut up its' ass, pull it back out, then eat the peanut. That was disgusting, it about made everyone in the bar sick.

The man came out of the restroom, and the bartender was mad and threw them out again. He told the man about the disgusting thing the monkey had been doing with the peanuts.

The guy said "Well, yeah. Ever since that cue ball last year, he's been checking everything for size".