One of the best I've had was with Tyler Flowers of all people. I had a broken, game-used bat of his and handed it to him to have it signed. He was joking that he has signed so many during his session, and didn't know why the Sox were getting rid of all of them. It was authenticated so it had a MLB holo on it, and I had looked it up before hand to see the result. He wanted to know what the result was, so I told him. Ground into a 6-4-3 DP against the Twins. He sighed and goes, "yeah... I do that a lot."
Thomas, Pierzynski, Ozzie, Buehrle, Wise, Delmonico, Palka, Anderson, and Courtney Hawins have all been great too. I've probably met close to 200+ players at this point, so I have quite a few stories/interactions.
Some of the worst have been Sale, Aardsma, and Jenks.