"Meet my friend Roy" vs. "Meet my friend, Roy"...

The first sounds like you're telling someone to meet your friend who's named "Roy." The other sounds like you're telling Roy to meet your friend.

If I were not due to turn into a zombie in four minutes, I'd dig out my Little, Brown handbook of grammar / writing and find a definite answer.

Sometimes these conumdrums can be avoided by reordering the sentence. But not by a Zombie