Top definition
A slang term for a hangover.

Originates from the brown bag that alcohol is placed in at liquor stores and the tendency to attribute a hangover to some sort of illness.
"Joe called in sick this morning"

"Man that fucker isn't sick he just has a case of brown bag flu"
by ACRanger April 26, 2010
Get the mug
Get a Brown Bag Flu mug for your Uncle James.