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The day after a night of excessive binge drinking of alcohol, in which one is so hungover that the activities/responsibilities for the day are similar to that of an infant. Namely, eating, sleeping, and shitting.
Mikey- "Holy shit, I feel like hell today from drinking all those 151 and Coke's."

Me-"Dude, looks like you're gonna have a Baby Day."
by Jimbo Slice 60 June 22, 2010
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