To joke on someone, to pull a fast one; to be mischevious and devious in intent and nature; to fool someone or lead them on thinking one thing, only to have them unpleasantly surprised about the true result
Guy puts in work all night for this girl at a party. As they go upstairs and get ready to have sex, the girl passes out before anything happens. The guy's response, SHANANAGAINS.
When two people leave a large group and make strange noises that lead their friends to believe that they are having shananagins. (a.k.a. sex). Generally used when describing what two people were doing to make fun of them.
Paul: hey sara, want to go get some soda?
Sara: sure
Jim: oooh I see! you guys are gonna go have some shananagins! I see how it is!
Brad: Don't into too many shananagins!
Paul: ugh er erm NO!