I've been dating a girl for a few weeks. As expected there was a bit of initial resistance from her social circle to accept "the new guy" but it took not more than a drink and a few minutes of funny chitchat to break it. For the most part I can "blend in" quickly (PUA social skills go a long way.)

The exception being her gay best friend (this guy > ) He barely acknowledged my existence. It definitely felt intentional, and there was no lack of trying on my part.

It's been going great with the girl but if I can win him over I would score major points. The "kill them with kindness" approach usually works for me but how do I blast through HIS bitch shield?

He has decided not to like you, for some reason. Probably due to some preconception, but it can be any reason. Maybe you gave him the wrong impression. I ususally avoid such people since they don't contribute to my well being.

Try asking his friends, including your target, "he doesn't like me, does he?", and see if they can shed some light on the situation. You can try to build rapport with him by confirming his feelings and speak it out loud. For instance, if someone invites you to something, e.g. an after party, you could answer with a playful attitude "I would love to come, but that guy scares me, he doesn't like me and I don't know what I've done wrong". That will hopefully loosen him up a little bit. The keywords here are "he doesn't like me", but the context may be totally different when you say it. Don't repeat it more than two times though. That is just annoying.

If these words gets you his attention, you will have to be ready for some crossfire, or shit tests if you like. Whatever he says, don't try to please him too much. Just follow the rules of the game as you've learned them, as if he is the girl this time.