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Nashies: a proclamation of intent to cause mischief. Sometimes used as a question, “nashies?,” inquiring as to likelihood to cause mischief. And sometimes used as an exclamation, “nashies!,” after mischief has occurred.
Known Origins: My brother (On live the Vikings) purchased a Game Cube and Super Mario party for us for Christmas. Ian and I prepped our partiers (he readied Mario, and I readied Boo) for a good game. For some wonderfully fun reason, I changed Boo’s winning test to read “Nashies?!” I have also been known to say “nashies!” whilst nibbling on someone or in the dead of night when I cannot sleep. The term has stuck for all those mirthful moments when you don't know what to say but are simply driven to fill the air with mischievous musings.
Example: We are going to the library, so you will have to leave all nashies at home. I'm sorry, but they just don’t understand nashies there.