The thing that irritates ISU fans so much is that most Northern Iowa fans (my in-laws are an exception as they're truly UNI fans above all else) are bigger Iowa fans than they are fans of their own school, so the whole Cy-Hawk thing seeps into the ISU/UNI dynamic. ISU fans mock them for not really being fans of their own school, and UNI has kind of a reputation of being a suitcase school where everyone leaves town on the weekends to either go back to their home town (usually some small town in northern Iowa), or party in one of the other college towns.
So most UNI fans are bigger Iowa fans, and are way more obnoxious about their Iowa fandom than people who actually go to U of I. UNI's coach openly talks down about ISU, and just showers Iowa with praise - even when they play them. UNI has literally TRIED to lose to Iowa when they had them on the ropes, lest they give their beloved Hawkeyes a black eye, but they fucking live for beating ISU (even though it really doesn't make a shit in their ability to win the MVFC or play in the FCS playoffs).
I fucking hate playing those guys, and losing to them is the absolute worst. Plus, it's historically a guarantee that ISU isn't going to a bowl game.