If I wasn't a ND fan, I'd be a fan of Texas, Clemson, Georgia, or Florida. At various points of my childhood, I was enamored with those programs at one time or another. I feel that way about a handful of baseball teams too.
Teams I will never cheer for: Michigan, Purdue, Penn State, Ohio State, Bayou Brian.
OSU vs UM game: I always prefer one of two outcomes: 1) a game in which both teams look like absolute dog shit and Michigan loses or 2) a game in which OSU beats Michigan by 50.
Oddly enough, I don't hate USC. I hated losing to them during the Carroll years, but never truly hated them. USC @ ND tailgates are some of the best times I've had.