I used to play competitive chess, and met former World Champion Mikhail Tal at a competition. He didn't speak much English that I know of, and I didn't speak Russian, but he signed my scoresheet for a game I happened to win

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I was in the audience during a taping of
The Phil Donahue Show and met him afterwards. Too bad the topic that day (ca. 1988) was "How To Get A Man" . If I'd come the day after, he was interviewing John F. Kennedy Jr.
My sister-in-law used to live in Carmel, California and worked in a department store. One day, then-mayor Clint Eastwood came in and asked her where the towels were. All she could say was "Hi....". He was really cool about it, and laughed (and found his towels).