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Learn how football works
I'm not going to lie to you: if you're part of a typical American family, some flavor of football will be on TV for much of the weekend. Many geeks have resisted the allure of the sport just on general principles, but if you don't want to ignore your family entirely, you might want to learn the basics. This excellent thread on geekculture.com breaks down the rules of the game quite nicely.
Thanksgiving is right around the time that the question of who will be college football championship heats up. With dozens of teams in the NCAA's top level and no playoff system, do you know how the two finalists are selected? Math! Lots and lost of math! Master the devilish formulae and you will have definitely have something of interest to contribute.