The excess skin of your ballbag when it sticks to your inner leg on a hot day. When spreading your legs the skin streches and looks like a Batwing! All veiny and stuff!
Fucking hell mate I've got proper batwing.
Shit it's hot out! Ive got batwing and everything!
Cross your legs mate, looks like you've got some batwing there!
You know its hot when you've got batwing.