
I don't think it was the mustache

. I think that if you had concentrated on conversation with the other girl and included the previous girl it would've been okay.
All a matter of pulling the new girl into a new conversation and taking hold of the situation. The key is to choose your target, and focus on that in a way that is under the table. By capturing the new girl's attention, it shows your alpha male dominance (not I'm a meat headed cunt that will bash anything, but just using your intelligence as a tool).
Just simple conversation of getting to know her shows that you're actually interested in their friendship and their relationship together. Also, it opens up opportunities of understanding how both of their personalities work as friends. It's more of a social experiment but I've always found that it works and it impresses your "target" when you actually try to get to know their friends and that you're not afraid to adapting to different situations.
That's how I see it anyway.