Suppose as a 24-year old Saints fan I've been blessed (balanced out by Everton however).
Some would say 70-0 at Leeds but oddly I look on that fondly, I was at Headingley that day and the Saints fans just gave up after 20 minutes (about 15 after the team) and were just having fun on the West Terrace...even the youth team spankings at Bratfud were a laugh, especially when we were 4-0 up for a while
Probably Murrayfield in '02, although Cardiff '04 healed those wounds somewhat.