For me, one thing is simply how friggin' HARD they can get. When I was younger, mine was hard like a steel pipe, and that always fascinated me. Also the variety of shapes & sizes boggles my mind, i mean really, sizes ranging from like 3" up to like 11"??! What other part of the body has such a wide size difference? Also, the fact that NOTHING about a man's body can predict how big his cock is when it's erect, not even how tall he is, I call it "the great equalizer." One example is this dude in college who was on the football team, muscles everywhere & all, with an avg size cock soft, but one of the thinnest i've ever seen. Also, cockheads fascinate me, I mean why are they even there? Seems like they're a built-in jelqing aid Anyone else?