Top Definition
A holiday that takes place in the month of October that entails dressing up as penises and going trick-or-treating.

Also known as "Halloween".
Matt: "Hey bro, what are you dressing as for Hallopeen?"
Bob: "A penis, of course. I plan on truly celebrating Hallopeen with spirit this year."
by Cuddlybutdeadly October 09, 2010

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