If your girlfriend hates all your friends or your friends hate your girlfriend you can pretty much count on it not working out. This is true for a number of reasons:

1. You choose your friends based on how well you will get along. So it is reasonable to assume that if your girlfriend and friends don't get along that you will eventually not get along very well with her.

2. When you have a crazy wrong doing woman your friends will realize it months before you do.

3. Alienation will occur either between you and your girlfriend or you and your friends. The reason this is bad should be reasonably obvious.

Note: I can only assume this also holds true for boyfriends.

Reply to Uberfetus:
You are too right, but I doubt that one node is room enough to discuss all the problems that can occur in a relationship.