Well, this has always been one of my favorites:

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Juan comes up to the Mexican border on his bicycle. He's got two large bags over
his shoulders. The guard stops him and says, "What's in the bags?"

"Sand," answers Juan.

The guard says, "we'll just see about that. get off the bike." The guard takes the bags and rips them apart; he empties them out and finds nothing in them but sand.
He detains Juan overnight and has the sand analyzed, only to discover that
there is nothing in the bags.

The guard releases Juan, puts the sand into new bags, hefts them onto the man's shoulders, and lets him cross the border.

A week later, the same thing happens. The guard asks, "what have you got?"

"Sand," says Juan.

The guard does his thorough examination and discovers that the bags contain nothing but sand. He gives the sand back to Juan, who crosses the border on his bicycle.

This sequence of events is repeated every week for three years. Finally, Juan doesn't show up one day and the guard finds him in a cantina in Mexico.

"Hey, buddy," says the guard, "I know you are smuggling something. It's driving me crazy. It's all I think about. I can't sleep. Just between you and me, what are you smuggling?"

Juan sips his beer and says, "bicycles."

Greg the White wrote:

What do you call a sleepwalking nun? A roamin' Catholic. (Roman/roamin' hurr).

In that same spirit, here's a classic groaner from the Disneyland Jungle Cruise script:

Q) What do you call it when you have a dock on your right, and a dock on your left?

A) A paradox!

Still makes me smile every time.

DarknessDeku wrote:

What's worse than 10 dead babies in a trash bag? One dead baby in ten trash bags.

I feel so fucking wrong for laughing at that lol. What is it about morbid jokes like that that are so funny, even when you know they shouldn't be?

Ross Rifle wrote:

Try laughing at this one: Why do you feed a baby into a blender feet first? So you can stare into its eyes while you masturbate. I've recommended therapy to my buddy that told me that one.

Hmm, yeah, not so funny. But honestly, that doesn't feel like a punchline to me at all; just a series of gross images. Which, granted, can sometimes be over the top enough to induce laughter, but not for me in that case. The whole thing with jokes is a twist, or destruction of expectation, in the punchline. In the "babies in a bag" joke above, for example, a large part of the humor (I think) comes from reversing the initial setup in the punchline. ("Ten in a bag" vs "one in ten bags".) The blender joke has nothing like that. Subtle, yes, but there's a reason people laugh during "Scream" but not during, say, "Saw" or "Hostel," despite the fact that there's a hell of a lot of gore and innocent people getting killed in all of them.