The act of rubbing your hand on your balls,mainly after you've been sweating like crazy, then you rub your "flugen" on your friends mouth and face, and scream out what you've just done so everyone else knows why your friend is gagging.
Also used as a means of confirming comprehension of such information.
Jenny performs oral sex on Bjorn and when she finishes she wants to know if Bjorn enjoyed it, so Jenny says, "Schmurgen?" and in response Bjorn says,"Schmurgen."