Might not even make top 10.
1. Kasay kicking off out of bounds in the Super Bowl.
2. Kerry Collins being a drunk washout, then leading the Giants (my dad's team) to a Super Bowl.
3. Trading a second round pick that eventually became the #33 overall pick for a FCS running QB, who would then be groomed as a failure of a slot receiver.
4. Delhomme meltdown against Arizona.
5. Twenty years of existence and no back to back winning seasons.
6. Winning game 1, then losing 15 in a row in 2001.
7. Andrew Luck proactively avoiding the team.
8. Drafting Jimmy Clausen. I knew he would suck, just knew it. I have witnesses from when the pick was made.
9. Somehow being the worst team in the league AND headed for cap hell at the same time in 2010.
10. The Rae Carruth and Fred Lane things happening within one year of each other.
There is a long and healthy tradition of disappointment here. Those are my top items; sure I left out some good ones. YMMV.
1. Seeing Steve Smith in a different uniform.