When a gentleman places his scrotum and testicles inside the anal cavity of the young lady thus acquiring said "brown bag". The coated scrotum is then placed into the womans mouth thus creating a "Brown Bag Lunch".
After a stimulating night at the opera Theodore surprised Emily with a Brown Bag Lunch. As per Jeeves, the butler, cleanup was "ghastly".
an event in which an individual is defecating in a porta-potty and another said person proceeds to tip the potty over causing a situation in which individual #1 is wallowing in his or her own excrement
I was taking a dump, when I felt a nasty thump. I felt the potty tip, and I was covered in shit. Needless to say, I wasn't hungry, but I got a brown bag lunch.