The day that comes after Thursday and before Saturday.
As the name suggests, this is the day of the week when GUYS hang out and don't have to listen to their Girlfriends.
Girl: "Do you want to have some sex tonight?"

Boy "Cant't. Guyday"
by Roganator November 29, 2010
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Like black Friday, except you steal everything so you're not getting a good deal, you're getting a GREAT deal because it's all free.
by Megawreckindaddyhitler November 23, 2018
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