This was a tough one. I was at the '93' fiasco in the Big House, so I had to go with that one
I would rank the MSU loss right up there too, especially leading 23-9 deep into the third quarter.
Another one that could have gone on the list was the game against UM in the shoe (80 I think) when Art ran the option on 4th and 1 at the goal line at the end of the game. It was in and win or get stopped and lose. If Art makes the pitch we win. He doesn't and sticks his head in the line and gets stuffed. Argh............