stop me if you've heard this one already...

A guy walks into a bar with his pet monkey. He orders a drink and
while he's drinking, the monkey starts jumping all over the
place. The monkey grabs some olives off the bar and eats them,
then grabs some sliced limes and eats them, then jumps up on the
pool table, grabs the cue ball, sticks it in his mouth and
swallows it whole.
The bartender screams at the guy, "Did you see what your monkey
just did?"

The guy says, "No, what?"

"He just ate the cue ball off my pool table - whole!" says the
bartender.

"Yeah, that doesn't surprise me," replies the patron. "He eats
everything in sight, the little twerp. I'll pay for the cue ball
and stuff."

He finishes his drink, pays his bill, and leaves.

Two weeks later he's in the bar again, and he has his monkey with
him. He orders a drink and the monkey starts running around the
bar again. While the man is drinking, the monkey finds a
maraschino cherry on the bar. He grabs it, sticks it up his butt,
pulls it out, and eats it.

The bartender is disgusted. "Did you see what your monkey did
now?"

"Now what?" asks the patron.

"Well, he stuck a maraschino cherry up his butt, then pulled it
out and ate it!" says the barkeeper.

"Yeah, that doesn't surprise me," replies the patron. "He still
eats everything in sight, but ever since he ate that damn cue
ball he measures everything first!"