A guy that you are "just friends with". More often than not they secretly like you. ;)
I have a friend who is a guy.
I think he secretly likes me.
I don't want him as a boyfriend.
Therefore he is my guy friend.
Used by Docter Evil from Austin Powers. Means "Who cares?"
Bob: Whaaah I lost my cordless phone and now the phone keeps ringing and ringing and ringing... :(
Alfred: Boo frickety hoo!