Fortepian można zasłonić lecz słonia nie można zafortepianić.
to me, it loosly means that not everything goes both ways, or, not always the reverse is true. It's a play on words, based on the fact that "to cover" and "elephant" sound the same in Polish.
But back to the song! I just found out that it's like 4 years old, and it's the funniest thing I've heard in along time. Polish men with a biting sense of humor is a new discovery for me!
No disrespect to present company. Yo. :)