The act of drinking a beer (or brew) while on the toilet, preferably taking a poo. It is a combination of "brew" and "poo".
Person 1: Man, I really need to take a poo right now but it feels like a doozy that might take a while. I don't wanna just leave my beer here and let it get warm...
Person 2: Why dont you just take the beer with you and enjoy yourself a nice Broo
, it will make time fly!