Woah woah woah, you're getting ahead of yourself there I never said "just rub your dick on her that'll get you laid" this isn't a porno, although that might work... I meant rub it with your own hand once or twice, or "adjust" yourself when you're rock hard. Make it obvious but subtle, like a magicians sleight of hand, your hand going towards your cock is meant to grab/drag her attention towards your mighty fine (20 inch obviously, mines 21 so I'm bigger) penis.
I have no faith in the "rub my cock on her" theory unless you know it's a massage and you're straddling her.