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.
Crazy shit that happens for no reason.
You are always getting into so dam many shananagans, when will you learn?