The often heard avalanche of faecal matter erupting from someone's bowels in a public bathroom...
A: "Dude i was just in the bathroom and the place shook with a damn brown avalanche!"
C Walks in with a pleased grin on his face.
A: "Feeling relieved?"
C: "Oh yeah."
A brown avalanche is the fecal equivalent of a golden shower.
Hank gave Cecilia $50 for a brown avalanche.
She climbed to the top of a stepladder and gave him his money's worth.