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?
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!