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1.
Laughing out loud at something.

I've never heard this outside of Delaware.
"I started baggin up when I heard my teacher's name was Mr. Doody"
by Drake Dwornik May 11, 2004
 
2.
An urban term (used mostly in the midatlantic area-originated in Delaware) used to describe laughing or shared laughter. To bag up, bagged up, etc.
That guy was walking down the street and ran into a pole, and we started baggin' up!
by TTWhy February 10, 2009
 
3.
Laughing out loud
He started baggin' up when his friend tripped and fell in some mud
by AK July 22, 2003