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

A word used when one person claims he/she will do/say something and you think they won't.The penalty for not doing what they said they would (when a shananagains is called ) results in them being hit in the balls / boobs by the shananagee , ( person who calls shananagains ).