Loads of contenders over the years, but for the actual experience, getting relegated at Villa Park was worst for me. I had a canny trip there and never really considered that we might actually get relegated, and when we did it was the culmination of a dreadful season. It was only at the time that it was properly shit mind, as in retrospect I loved the season in the Championship.
The trip back from Cardiff after the Semi Final was absolutely rubbish too as it took forever and I had a rotten sore throat so didn't want to fall asleep in case I snored on the coach.
Special mentions for the gigantic rages that Partizan & Lisbon caused.