Definition: To go crazy; to lose your mind.
Example:
1) Maria wigged out when she found her husband in bed with her best friend.
2) I hope Tom doesn't wig out when we tell him we lost his dog.
Etymology: The idea behind the term is that so much activity is going on in your brain that your hair (a 'wig' is artificial hair) might jump off your head. The term can be positive too - you might 'wig out' when you hear really good music, for example.
Synonyms: lose your cool, flip your wig
