rock in your sock

When you're sat there jerkin and it just doesn't cum.

Demetrius: "Hey bro, you were in my bathroom for a while, the fuck were you doing in there?!"
Alejandro: "Sorry dude, I just sat there with a rock in my sock."
Demetrius: "Probably a good thing you had a rock in your sock since it's my fucking bathroom you bitch!"
Alejandro: "Nah man it's cool, I splooged in there last week!"