I was having lunch with a close friend in a crappy Mexican place on Telegraph Ave in Berkeley, California; it must have been about 1983. The restaurant was called La Villa Hermosa, and is long gone. (There is a photo of it here.)
Sitting at the next table was a bearded man who looked familiar. I studied him carefully, while eating my refried beans. Eventually I figured it out. I nudged my mathematician friend gently under the table and said softly, "Hey, that's Jerry Garcia over there."
She looked over doubtfully, and said, "That's not Jerry Garcia."
I insisted, "Yes, it is."
So my friend, who was never one to observe social niceties despite being only a little more than five feet tall, stood up, walked over, put her hands on her hips and demanded of him, "Are you Jerry Garcia?"
He looked at her, held up one hand (clearly missing part of a finger), and said, "No, Jerry Garcia is missing a finger on the other hand."
She came back to my table, satisfied, and announced smugly, "See? I told you so. That wasn't him. Jerry Garcia is missing a finger on the other hand."
I swear it's true!