Wow, okay, so you use "playing the skin flute" to mean masturbation? I always heard it used to mean giving a blowjob.
This had me and a bunch of other workers at the aforementioned ice-cream/coffee shop in stitches a couple of weeks ago, actually. This guy Jeff, who's a generally nice but a little bit creepy guy (I'm the oldest person who works there as a worker, at 26, except for Jeff, who's like 43) who has been known to make inappropriate comments to the girls who work there, was talking about playing musical instruments when he was in sixth grade or so.
"But my favourite instrument to play was the skin flute," he said, winked, and dashed into the back. All the girls just stared.
So I guess he meant the Jake-meaning, not the one everyone else assumed he meant.