It was a manga art two guys who end up having sex and to determine who gets to top they compete on who has the smallest penis. I don't remember much from this because it has been a few years since reading it(can't remember if it was a oneshot or a full volume--> leaning toward oneshot) If I recall correctly the eventual uke is the one who proposed choosing the smaller penis as top as he had a rather smaller member, the eventual seme (i think) described his member as the size of a cocktail weiner(or something like that) but it ends up getter pretty big as it gets hard.[both weird, specific things to remember, even more so if they were remember incorrectly, but...]