Why do certain men talk to men about their girlfriends as if theyre not there?

I think it's a combination of two things. First, the very old courtesy of never speaking directly to a lady but only through the gentleman, who was her "protector" -- the man ordering food for the lady in a restaurant is a holdover from that. Second, I think it was simply bad manners. Combine the two, and you can get what happened to you.