For me nothing was worse than the 1970 game against USC when Theismann was phenomenal and Jimmy Jones played the game of his life especially in the first half. They were making unbelievable catches on every pass Jones threw and he was not known as a good passer. The rain in our comeback attempt was heavy and relentless or we may have pulled it out anyway.
The 1974 game was incredibly upsetting also but I was out of school by then so it hurt badly but not quite as much as 1970. I never saw a momentum switch like that one in 1974. They were probably a little better team but we had them in the first half and if we would not let them have that late touchdown in the first half they would have died.
Also Montana's great comeback in 1978 was one of the worst reffing, blatant bad calls ever made when we caused Paul McDonald to fumble and they said he was throwing. Replay would have changed it to a fumble. Oh and
The fumble by them in 1982 which we recovered and would have made Faust's record over his career against USC 4-1.
This is all in descending order but they were all influenced by momentum switches and bad reffing.