My wife grew up a Steelers fan. She isn't a really die-hard fan, and I've worked my ass off to convert her. All of her family are Squeelers fans as well, and I'm constantly subjected to it. They are very good about it, and my father in law has even started pulling for the Browns when they aren't playing Pittsburgh. i however cannot return that favor.
Also, one of my grandfathers was a Steelers fan. When i was about 5 or 6, he gave me a Steelers knit hat that had my name sewn on it. he was a great guy, but the hat gives me the shakes and makes me want to vomit. i still have it and keep it as a reminder of how close i may have come to falling into the dark abyss of squeelerdom.
I'm sure there are plenty of families that engage in this "civil pigskin war". I'd like to hear any similar stories any of you may have.