Definitions by Kingsbury Brothers

Flap Jacking 

A tandem masturbatory technique in which the participants lock arms at the elbows whilst gripping the shaft of their penises. They then flap elbows like a bird in synchronization to most efficiently share the work of jacking.

I jerked off with my friend, but it wasn't gay because we were flap jacking.

Flap Jacking by Kingsbury Brothers February 6, 2010