Interesting concept and very addictive (both reading and creating).  A website (and subsequent twitter handle) that showcases punchlines sans set-up.  Check it out and give it a shot:

http://www.orphanpunchlines.com
https://twitter.com/#!/OrphanPunchline

I would love for some creative (and funny) folks to come up with some of their own.

Roy Templeton
Orphan Punchlines

Here are two examples to get things going:

”...And with one small gesture, Jerry realized how lucky he was to have Jimmy the Needle as a cellmate.”

”...Dorothy turns to the Tin Man and says, “Bet you can’t get THAT from the Wizard.’”

For more examples - or to submit your own:  http://www.orphanpunchlines.com