The most annoying "feature" of penis is that it hinders your life just simply "hanging around". Now, when you are going for a run, say for two hours or for a marathon, you'll have a penis swinging between your legs. (Fair enough, females have parallelly tits bouncing on the chest..) I've seen people with a wounded penis after a marathon and it's not hard to imagine the horrid of that scene.

You may think it's nice to have a handy penis when you pee standing but just wait until you close your zipper. Who's the one that reminds you about its existence!?
Of course, those who haven't experienced the pleasure of having their dick sticking in the zipper may find it funny but as an utilitarist it's hard to find this malicious delight being greater than pains caused by zipped cock.

If genetic engineering has anything to offer they really should create a removable penis!