"Hi guy I don't know across the street!"
I was about 13 and saw Weird Al Yankovic walking across the street from me. I lived in a small town in Canada so I was pretty surprised. This would have been right around his 'Amish Paradise' days and I was a big fan, so I waved and yelled: "Hi Weird Al!"
He sees me and waves back madly, yelling: "Hi guy I don't know across the street!"
Then we just both kept going our separate ways. I hear he's a ridiculously nice guy to talk to as well, so that's nice.