A pic
A pic is when someone asks for a pic and you know they want to trade nudes. It's like a kid trading lunch money for candy, but with your privates.
He said, 'Pic for pic?' I said, 'You better send me a good one.'
She asked for a pic and I sent her a pic of my privates.
He said, 'Pic for pic?' I said, 'Only if you send me a good one.'