I knew a guy once who was short, very skinny, and endowed like an ox. He had almost no sex drive. But when his cock got hard, it was painfully so and his erection lasted for hours. A true eight-incher, he was so short that his erection reached almost to his rib cage.
I once had the honor and pleasure of seeing him come back to his dorm room drunk as shit, and horny like no one's business. In time, he collapsed on a bean-bag cushion on the floor, naked, caressing and fondling his huge penis and moaning, "It's so big, it's so hard... oh, god, it's so big and hard, it hurts, oh it's so big..."
It was like that scene in Total Recall where this monstrous alien comes out of the man, and takes over his body. That's what this guy's dick was like: Something that completely dominated him, and turned him into a raving masturbator.