A joke played on an innocent victim, where several people agree beforehand to laugh at a completely pointless joke involving elephants, polar bears, etc. in a bathtub with the punch line "no soap ... radio". The objective is to see if they can get the victim to laugh along so he won't look like he was too dumb to get it. If he does, then everyone stops laughing and asks the victim what's so funny, and gets a good laugh at his embarassment.
An awsome joke in which the joke is on one of the listeners.
The teller will have a group of friends who know what is going to happen. The teller then asks somone who is not in on the joke if he would like to hear a joke. The teller tells a story that makes absolutely no sense and is not humorous, and finishes it with the line "No soap, Radio!". The friends in on the joke then burst out into laughter.
The friends in on the joke then get to see the reaction of the friend not in on the joke. Will he laugh at a pointless joke to try to fit in, or will he make an ass out of himself trying to understand it?
Teller: ... so there's this elephant sitting in a bathtub and he says to the gorilla, "No soap, Radio!"
People in on it: Ha ha ha!
Not in on it: *unsure* Ha, ha?
All others: Ha, moron.
Definition: 'you're full of it', 'whatever' or 'you're not that cool'. Soap is a valuable item in jail. Having a good bar of soap makes you a bit cooler, better/luckier than the rest of the inmates.
"I don't know why it's taking him so long to hang that new front door, damn, I would be finished already!"
His friend: " Oh you think you can hang doors now hu..? Psssh. Ha. You Ain't Got No Soap. "