I'm surprised no one has mentioned the 2018 Northwestern game in Evanston. Up seven with a minute or so to play, Northwestern with no timeouts, and (imagine this) a coffin-corner punt that left Northwestern's offense 99 yards from pay dirt. A boatload of missed assignments and holding calls later, they're in the end zone. Nebraska loses in overtime, assuring that homecoming game would go down in Wildcat history.
Another one that hurt was driving out to Nebraska with my wife and daughter for what was supposed to be the first game of the Frost era, only to be preempted by lightning.
That was a disappointment, but at least they didn't lose!