Zipper fear

In a strange turn of events at my house, Luke is terrified of zipping up his zipper. I went to put his jeans on today and he didn't even want me to button them. He jumped away and said, don't pinch me. I said, "Well, why don't you do it yourself then." Luke replied, "Okay" and proceeded to squeeze the snaps together unsuccessfully. He thrust his pelvis out at me where I was sitting on the floor, indicating that he was ready for my help. I said, "Are you sure?" He nodded. I said, "Hold still. Buttoning your pants doesn't hurt." I buttoned his pants and went to zip up his zipper but he let out a squeal and jumped away saying, "nooo." I looked at him like he was crazy and he said, "You'll hurt my penis." He jumped around some more. I said, "Good heavens! Who zipped your penis in your zipper?!" He didn't answer but put his hand over his crotch so I couldn't reach the zipper. I continued, "Honey, if you're careful, zipping your zipper will not hurt your penis." He seemed unconvinced and when I reached toward him again he shied away. I said, "Sweetie, you can't go around with your zipper down all the time. I understand that it would hurt very much if your penis got caught in your zipper, but you still have to zip up your zipper. Just be careful." I reached toward him again and said, "Watch." He squirmed and made that "eh, eh, eh!" noise that kids make when they don't want to do something or they think something is going to hurt. (He makes the same noise when I go to pull off a band aid.) So, I gently reached down and CAREFULLY pulled up his zipper. I only got it half way up because he jumped away. I again tried to reinforce the idea that he has to zip up his zipper at school. His response was, "Why?" I said, "No one wants to see your underwear. You just can't wander around with your zipper undone. There's a reason they make it so that your zipper zips up." Luke still seems unconvinced and I'm certain he'll continue to spend the rest of the day wandering around with his underwear peeping through his unzipped zipper hole. Aside from that, my biggest concern is who zipped his penis in his zipper and how long will it take for him to recover???? Poor kid.