Probably Ozzie at Old Comiskey when I was really young, like 7-8. He used to sign after the game outside in one of the parking lots sometimes and that night he was out there so my dad took me over and although I didn't get anything signed I shook his hand and all that. Very young hardly have much memory of what he said but the moment after the game has stuck with me.
Not a player but after Avi laced a ringing double a couple years ago in spring training I was about 20 feet away from Steverson and asked him why he couldn't hit like that more often. Steverson never flinched, looked me in the eye, and gave a big old shrug.