Great fan/rivalry stories

Does anyone have any great rivalry stories that they were personally involved in? I'd like to hear some good ones. Here's my favorite: I grew up in Flint, MI, so half of my family and friends were Sparties, half Wolverines. Every year, my aunt and uncle (who my family was really close to) would go to the UM-MSU game, and every year my dad, brother, and I would sneak over to their house with sidewalk chalk and chalk up their entire 150 yard drive-way with anti-MSU and pro-UM propaganda. But, when I was 12, UM won a close, hard-fought game (I don't remember which one) and my dad, brother and I did the same thing, but we also brought our push-mower and mowed a block M into their lawn, which was a perfect M that was visible from the main road. Accidentally, we cut the grass too short, and the grass burnt and died, leaving a block M in these poor peoples' yard until the snow fell. They literally (and I mean this LITERALLY) didn't talk with us for 4 months after that.