The worst I can remember was being 4-0 down to newly promoted Sunderland inside 35 minutes or so, what was even worse was that Ed De Goey was Man of The Match up to that point and the scoreline flattered us.
There are many others, the 2-1 against Spurs where Cech prevented what should have been at least a 5-1 scoreline, Pavlyuchenko missed a few sitters and one on ones or we could have been staring at a record defeat for us in the PL.
5-1 loss at Anfield with Patrick Berger getting a hattrick. 4-2 home loss to Wimbledon and 2-0 loss at Valley Parade.
The 1-1 draw with Fulham on Boxing Day last season was up there though, possibly the worst atmosphere and football game I've ever watched at the Bridge.