Blue T-Days are the two days in the week that start with "T" as in Tuesday and Thursday, those are the days you wear blue underwear or panties.
Girl:"What is today???"
Guy:"Hold on let me check." *glances down at their underwear real quick* "Tuesday or Thursday."
Girl:"Blue T-Days?"
Guy:"Yep."
Girl:"Oh."
by Dalyena September 10, 2015
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