When a female slides her hand up the shorts (preferably boardshorts) of a drunken, passed out male and gives a nice little tug on his junk, soft enough such that he does not awaken but hard enough to wildly entertain the surrounding audience.
a wanger schalnger is a type of german sausage, but since it will be said very seldom in this sense, if you hear it anywhere outside germany, the likelihood is that the person saying it is referring to a penis.