A string walks into a bar. The bartender spots the string and hollers, “Get out! We don’t serve strings here!” Dejected, the string leaves.
Outside, the string ties himself into a big bow and frays his ends. He goes back into the bar. The bartender eyes him suspiciously. “Are you a string?”
“Nope,” says the string, “I’m afraid not.”
Actually, I got it with Mindfield’s explanation, Philster. But thanks anyway. 
Q. Why can’t you starve in the desert?
A. Because you can eat the sandwiches there.
No it’s just American pronounciation is required.
In UK there is a difference between d and t when spoken
Diz ass Ter and diss assed 'er are too far appart.
Une of mine, but for written use not spoken
“A legend is afoot”
Wow, no love for the sexual practices of architects and nuns, eh? In my meager defence, my enjoyment of these is not in the subject matter, but in how well hidden the double entendres are. I enjoy the aha moment of getting them (or more likely having them explained to me) and the actual humour involved (if any) is secondary.
I may have posted this before. Here’s the super-brief version: Guy reads an ad “Find out who you are, 123 Main St.” He visits, enters the main door and sees two doors one labelled “Male” second labelled “Female” He enters the male door and sees two more doors “Employed/Unemployed” …[fill in details with as many doors as your audience will tolerate before falling asleep or lynching you]…, until finally, after walking through that last door he finds himself on the street.
Come on, at least give it a try before revealing the spoiler:
After applying noting the labels above all the doors, you would have an insight into “who you are” fulfilling the promise of the ad.
This one is truly not funny. I offer it for use as a weapon against those you truly despise.
When reading the spoiler above, please remove the word “applying”
Well, I didn’t say it was funny – at best it was better than the nun/wears joke (thanks, Scarlett for explaining that, even though I’m going to try my best to forget it). But yes, some puns should never be repeated lest they kill again. Much like the one I read in Dirty Jokes Vol. II when I was a kid:
What’s the difference between a woman kneeling in church and a woman kneeling in the bathtub?
The woman kneeling in church has hope in her soul.
ducks
Oh! Oh! Which reminds me…
What’s the difference between a rooster and a lawyer?
In the morning, a rooster clucks defiance.
What’s the difference between Cirque de Soleil and the Rockettes?
The Cirque is a cunning array of stunts.
(I always have to think carefully before speaking these ones)
Why are there no aspirins in the rainforest?
Because parrots eat em’ all!
Sigh…and once again I debase myself:
How do you get rid of polar bears?
Get a penguin. It worked at the South Pole, didn’t it?
Mmm. I heard “made” as “mate.” Which also works, and is a bit dirtier.
Gestalt
There really should be a name for this kind of joke, where one only needs to say the first half of the punchline, because the listener’s mind can be counted to fill in the second half, which is the good part.
Another one along those lines, from the 1988 Presidential campaign:
What’s the difference between Republican women and Democratic women?
Republican women give their heart to Bush.
Better (and older) version:
Q. What’s the difference between pygmies and a woman’s track team.
A. Pygmies are a cunning bunch of runts.
This one took years for me to figure out:
A: Too bad about Professor Jones. He seems to have vanished; no one has seen him in weeks. Everyone thinks he must be dead by now.
B: I know. He always was a first-rate mind. Why, the last time I saw him, he was out in a boat, and when I called to him, he shouted out, “I’m thinking. I’m thinking.”
A. You fool! The professor lisped!
Technically it’s a spoonerism, though that’s just the mechanics of the punchline. I don’t know if the style of joke has its own name.
Really? That seems impossible to me: how can you make a final “d” sound different from a “t”?
My favorite, which isn’t so much funny as it is satisfying, almost zenlike:
The three cowboys saw their father was getting too old, so they took over running the beef cattle ranch. They painted the barn, they added a wing onto the house, they ran a state-of-the-art electric fence around the property. With all that work,t hey decided the ranch needed a new name–so they asked their father for advice.
“Call it ‘Focus,’” he said.
“Focus?!” the sons asked. “What kind of name is Focus?”
“Because,” said their dad, “That’s where the sons raise meat.”
(Say it aloud. Meditate.)
Daniel
Voicing. “T” is an unvoiced alveolar stop; “d” is a voiced alveolar stop.
Consider “had” and “hat”: the final sound is different.
Right, but we’re talking about an unvoiced sibilant (ass) followed by an alveolar stop. How do you have a voiced alveolar stop following an unvoiced sibilant? And is this the nerdiest conversation ever to happen around the word “ass”?
Daniel
Hmm–it occurs to me that the “er” following the word “assed” makes a difference; maybe it’d be pronounced in England like “Ass dummy” as opposed to “ass tummy”?
I still can’t make “disaster” and “dis-assed-her” sound different without speaking them really weirdly, though.
Daniel
Hwuh?
The opposite of “A Tailor to Cities”, then. (We would pronounce the first “s” differently, of course, but it’s close enough.)
fetus,
Sand Witches, methinks.
LHoD, care to explain the Focus one?