Cardboard Socks

When a person is having a masturbation session, they are about to blow their load, but they haven't got something to unload into, they pick up a dirty sock and blow the load into it. They forget it's lying there for weeks, and the cum makes the sock harden like cardboard.

Tom: Dude, what is up with that smelly sock?

Jeffrey: Dude, I was lazy, I blew my big load into that sock last week and it's like cardboard now.

Tom: Cardboard socks!