I believe that most dogs are good judges of character. Perhaps Nebo is more discerning than most. He can probably sense that your friend's brother doesn't care for animals. (though how anyone could not like a beautiful fella like Nebo is beyond me) My sister's dog, on the other hand, really seems to dislike most straight men. He likes gay guys, but often barks and growls at straight men when he first meets them. How he can tell, and why this would be important to a dog, I have no idea. Once he realizes that we like the guy, though, he generally chills out and is very friendly to them. He is one strange little mutt.