It's quite common, so don't feel weird if you have it.
John entered a public restroom. Having not used the bathroom for a few hours, he really needed to. He didn't have time to reach a stall, and besides, they were all taken.
John decided to use a urinal. He unzipped his fly, and just when he was going to release himself, a burly man stands next to him to do the same. Meanwhile, John is standing there, afraid, confused, wondering what his penis' reaction will be.
He just couldn't. John went to his doctor to ask him why he couldn't urinate in a urinal whilst standing next to another guy.
There was only one thing.
John had penis fright.