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.
A word used by a middle school principle when finding one of his male students making-out with another female student in the backroom of the stage while a play was being performed. It might also derive from a little lepricon who once spoke of great things to myself and many others, yet the true form will never be known.
"Now David, I want no more of these shananagans around my school unless I be apart of it. Shananagans are against our moral code, and will be delt with by thy All Mighty" -Ron Wright