After you have a bowel movement, and you think everything has gone down, one little piece of poo will come floating back into the bowl. Since it has come back, it is a poo-merang.
In an Australian accent, "Krikey, I thought I was done, but I gotta flush again. I got a poomerang".
POO-merr-ang. Noun. Primarily used in corporate office environments involving the distribution of poo. Not to be confused with poo that rolls uphill or downhill, the poomerang is poo that is sent but inevitably returns at much higher velocity to its original vendor.
Nathan: "Why are these servers so messed up. The person who put these in must have been retarded!!!"
Rick: "Uh, dude. You're the one who put them in, and built them wrong. Now go fix it. Poomerang, man."
(pronounced like boomerang) a bowel movement that inevitably returns with a vengeance after prolonged postponement
to experience the return of an urge to defecate, often with increased intensity, after prolonged postponement
We'd better find a bathroom soon, it crawled back up but I know it's about to seriously poomerang on me!