The BYU game wasn't just a single call; it was the entire game, but concentrated in the 4th quarter with blatant holding never called. And it wasn't biased fans. Everybody in the stadium could see it other than the officials.
But the worst single call I can think of that I was present for was Ridley coming back in bounds to catch TD pass. That mis-call determined the entire game. I wasn't there, but the Auburn "first down" was absurd.