Longtime Monkey Island fans may remember this puzzle from the second game, where you need to decipher hand signals:
It's a halfway brilliant puzzle just because of the misdirection - after you figure it out, you either want to choke the designer for being so irritating or slap yourself for being so stupid. (Giving it away here, if you don't know it, would totally ruin the fun.)
So, anyway, much later in the game, when you're captured by LeChuck and suspended over a vat of acid, the evil zombie pirate gives a Bond-esque explanation of how his maniacal contraption will bring about your death, at which point you can ask a few questions. You can ask:
Why did I crack up with this? I guess it's because it's a totally random allusion to a puzzle so annoying that it had probably ingrained itself in your skull, and to be on the opposite side (the questioner instead of the questionee) while in such a dire situation is strangely appealing. The fact that LeChuck will give a straight answer - without the hand signals, even! - is just as funny.
Now that I've over explained the joke it probably won't be funny anymore, but maybe it'll ring some bells in those of you who've been through it before.