Used to work out at a gym in Boca Raton, Fl. Was on an aerobic machine next to a woman, but said to no one in particular "Hey, that's Derek Bell!", looking at a man on one of the aerobic machines in the row in front of us.
The woman on the treadmill next to me leans over and says "yes, that's Derek Bell. He's my husband.".
I approached him later on and he was very gracious and down-to-earth.
He was guest-driving in some Speed Channel races doing from-the-battlefield-in-car-commentating, and got spun around one race, driving a BMW M-Coupe. His car ended up stopped prone across the track and was walloped really, really hard by a car that could not avoid him and was spun down the track quite violently.
I saw him in the gym a few days later and said "Man, you took quite a ride", and he said "F---! Didn't I?"
Way cool guy, and listened patiently while I told him about my very un-exciting track days in my Miata. A true gentleman.
Pete Rose used to come to that same gym. Not such a gentleman.
Had experience similar to the gracious Mr. Bell, running into Brian Redman and Dan Gurney at the Amelia Island Concours D'Elegance, in different years. Very gracious people.
Extended my hand to Niki Lauda at the "place to be seen" hotel in Montreal during a Canadian Gran Prix F1 weekend, and was comprehensively snubbed. Didn't bother to do the same to Bernie Eccelstone, expected the same result.
Celebs are just like the rest of us. Some are nice, others not.
But my favorite celeb, at least in the racing world, is Scott Pruett. He's always been willing to talk. While these have not been exactly chance meetings, while at races he always seems to have time for people interested in him.