Sox - 1986 - I still cannot watch
Sox - 2003 - Next year made it palatable, but I did not sleep for three days. It was compiled by the fact that I lived in NYC and was a punching bag for so many...but 2004 was magical.
Sox- Buck Dent, 1978 - My first taste of Red Sox fandom. Remember this was just a finality after the "Boston Massacre" in Fenway during August I think.
Celts - 2010 - I don't think this compares to any Sox losses, because of the way the Sox found ways to lose and how they ripped your heart out. I LOVED this team, however, and was devastated by the loss, (the refs were horrendous) but it is a little difficult to complain when you have 17 Championships (8 in my lifetime). 2012 against the Heat was also terrible. Remember the refs in the first two games. I was horse from screaming.