Any kind of smell that seems like it came from a butthole, such as a fart, actual poop, etc.
You and your friend Anthony are talking:

You:Dude, wtf smells so bad? It smells like someone let out a poopy schmell!

Anthony: Sorry, I really had to let out a fart!
by The Schmelliest November 16, 2011
Get the Poopy Schmell mug.