Aside from the Cup Final losses / relegation- games which were already emotionally charged before kick off, my worst was:
January 2011, the 0-4 away loss to Leyton Orient, what makes it the worst / most depressing for me was how mundane it was, on a dreary grey day we turned up in East London and got battered by Leyton chuffing Orient (I know, I know shouldn't be so entitled etc etc), but there was a huge feeling of 'normalcy' about it, as in, nothing remarkable has happened, Wednesday had fallen so low that getting battered by Leyton Orient felt normal and that really got to me.
Only redeeming feature of the match came much, much later - I saw the first league goal of a certain H Kane.