Casually put her hand on your erection
From Create Your Own Story
As you lay there in silence, you reach down slowly and pick her hand up by the wrist. You pull it over just a bit and lay it down so that her palm rests over the lump of your hard on. You remove your hand from hers and wait.
"Seriously?" She whispers, removing her hand. "Dude, just go to sleep. Please."
You feel pretty stupid, so you do what you're told.