I had a similar experience twelve or fourteen years ago. Soundgarden and a few other bands played at a local venue, and I delivered a stack of pizzas backstage. I’d heard of the band, but I wasn’t into the grunge scene. As I turned a corner, I almost bowled some guy over, who was in the process of signing the back of a girl’s shirt. “Huh,” I thought, “this guy must be in one of the bands.” I described him to a friend later on, and it turns out the guy was the singer of Soundgarden.
One of my favorite celebrity stores involves a pizza delivery again, this happened in the early '90s. I was taking a pie to the top floor at the Fairmont, where the rooms cost a million dollars a night. As I was stepping out of the elevator, there was an older couple - in their 60s or so - waiting to get on. As I walked past, I made eye contact with the man for a second, and the thought flashed through my mind: “I know who this person is.” He immediately broke the eye contact and stared hard at the floor as he and the woman got on the elevator. The wheels were turning furiously in my head, and after a couple of seconds it dawned on me who the guy was. I turned around and raised my hand to point and say “You’re Dick Clark!”, just as the elevator door slid shut.