When a dude grabs his balls in each hand and stretches his scrotum up and out to the sides intending to replicate a bat stretching out its wings. The stretched out scrotum represents the wings and the head of the penis represents the head of the bat. Much like in nature, the bigger the wings the more impressive the Bat-Span! (Best results after a hot bath or hot-tubbing)
(Showing off to Girlfriend) Babe! Check out my Bat-Span!