Keanu Reeves.
I remember seeing him while walking through New York a long time ago when I was a young, probably very annoying pre-teen. I yelled out, "Yo, Neo!" And then I obnoxiously mimicked the bullet dodge motion from The Matrix. He looked back at me, laughed, and mirrored the same move in acknowledgement.
It's such a great memory because I feel like anyone would have been justified in getting annoyed and shrugging this stupid kid off, but instead he was a good sport and humored me. I'll never forget it.