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1.
A warning issued to friends or co-workers that a public facility has been polluted by human waste or flatulence, either yours or another person's.
Bart issued a Brown Alert in the first floor men's room this afternoon because he had Mexican Food for lunch.
by Philo Beddoe November 13, 2008
 
2.
When the urgency to defecate is so intense you're only mere moments from soiling yourself.
"I had to clench my ass cheeks together and hop to the bathroom because I was having a serious brown alert."
by Suck It Wilde September 02, 2009
 
3.
when someone has to take a major shit
oh god, look out brown alert comin through.
by danny and mason February 16, 2004