Verbally challenging back to your friends to give you added courage to do something that may be stupid or out of the norm.
Jim - "Man, you are not going to ask that fatty to dance are you?"

Bob - "Say I won't!"
by James Dorsey June 14, 2007
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Pretty much asking for verbal encouragement from somebody else. Egging another person on to say "you won't," so you'll have something to say you did.
"Man, you aren't gonna actually tell that teacher she's a fat bitch who sucks the mailman's dick behind her husband's back, right?"

"Say I won't. Say I fuckin won't."
by RiceBeani March 26, 2020
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