Families!

I just had to endure a weekend with a member of my family who is more thick skinned than a hippo. They merrily insult everyone, barge into people's conversations and personal space constantly, put everyone's backs up and generally cause trouble. I so wish I could just tell them where to go, but being a polite librarian I can't (though this weekend it was quite close) and I don't want to cause a family ruckus. But why should we put up with them?! Why do families always have someone like this? And what can be done about them (apart from moving to Australia)? Any suggestions would be welcome!