The act of or reaction caused by an individual with diagnosed or undiagnosed bipolar disorder, where as the individual changes emotions from happy or normal to sad or manic within an instant or a "flick of a switch" often with for no apparent reason.
Fred: "today we should order in pizza and have everyone come for lunch"
Me: "that sounds like a great idea"
Fred: "a great idea? it's my idea and if you think your going to get credit for it I will cut your head off and drink your blood".
Me: Fred has a classic case of being "Light switch Bipolar"