Shannanigans are similar to shenanigans, but in the case of shannanigans, they are perpetrated by Shan. It can be assumed that everything Shan does is shannanigans.
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.
You declare Shananagans on someone when they have cheaply tricked you in anyway.. whether it buying something, or doing something that you end of feeling scammed. Once declared, you are then allowed to take a broom and beat the crap of whoever you declared it on.
The towns people of South Park declared Shananagans on the carnival folk when they found out the prizes, food, and rides all sucked.. especially the line ride.