When someone says they are going to do something or did something but you don't believe them.

Can also be used as a greeting.
Girl: Did you eat cupcakes?
Guy: No.
Girl, I don't belive you, Show Me Your Weiner!

Friend A: OMG HI!
Friend B: Hi! Show Me Your Weiner!
by Unicorn<3r October 26, 2011
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