In contrast to the previous admittedly unfunny entries, here's a Japanese pun that is hilarious -- assuming, of course, that you have a (very) good working knowledge of the language. But, the pun being a slightly more elaborate affair, you need two people here: the punster and the victim.

Victim:
Hara hetta naa.
Gee, I'm hungry.

Punster:
Kintama namete minai?
Well, you want to lick my balls?

Victim:
???

Punster:
O-fukuro no aji suru yo!

<sound of all Japanese speakers in the audience groaning really, really loudly>

The catch -- explaining which, alas, takes all the life out of this -- is that o-fukuro no aji suru is a set phrase, much beloved by Japanese food product marketeers, that means essentially "Just the way Mom used to make it". So why is this funny? Because the literal meaning of o-fukuro, "Mom", is actually "bag" or "sack"... so the punster is claiming that his balls taste like an honorable nutsack, just the way Mom used to make them.

And a tip of the hat to Michael Cash for telling me this one.