This exact same thing happened to me a few years ago - I was with a buddy (who was rumored to have a monster dick) and we decided to try a hole in the wall rumored to have good sushi. They sat us next to the restroom and he made a joke about easy access from all the sake we were about to take in. Fast forward, we're both buzzed and about to leave (and drive to our respective parts of LA) and we both decided to take one quick leak before we headed out. There was only one urinal which he went to and I headed into the stall, and immediately made a comment about how gross it was and he suggested I join him, so I did. When he pulled out my jaw literally dropped and he chuckled, 'I know' was all he said.