One of the worst things about being friends with guys is being introduced to one of their new girlfriends. You're immediately seen as a threat, which is ridiculous because you've known these guys your whole life, and there's no way you can see any of them as anything but in a brotherly manner. Still, you have to make way more effort than normal to win this new girlfriend over, in a way that makes you seem like allies because you both have lady bits, but not so much that it looks suspicious sucking up. She doesn't like you because it seems like you don't have to make an effort to win these boy's affections: you're already part of the gang, while she as a newbie has to make extra good attempts to fit into the already pretty solid dynamics.