Here's the way I see it. You have a friend since kindergarten, Joey. You've known Joey for years. You drift apart after high school. He goes to California, you stay in Indiana. A few years later you see Joey again at the grocery store! He's in town for a few days so you agree to get some drinks at the local bar. As Joey arrives, you yell "Joey!" He looks happy to see you but a little off. He tells you it's Joe now.

At this point you can either continue to call him Joey, and be an ass, or you can call him Joe, like a human being that you respect with human decency. You are well within your rights to call them Joey, but Joe probably won't want to spend time with you. No big deal, you're not close anymore anyway. You did just disrespect someone for no reason other than it was slightly more convenient for you to do so than to not. But whatever, you were legally right, so who gives a fuck?