Upsets aren't about someone shit beating someone good, they're about the outcome that isn't expected coming to pass. Brooklyn Brawler beat Triple H, but it was obvious that Triple H would lose, because of his feud with Jericho. No, for me the biggest upset in recent history, and possibly ever would be Sheamus defeating John Cena at TLC in 2009. To illustrate this, look at the predictions thread made:
http://forums.wrestlezone.com/showthread.php?t=82551
As you can see, of the 21 predictions, 20 are for John Cena. More to the point though, almost everyone gave him maximum points, whereas the person picking Sheamus only scored it with the lowest value. In short, not only did people think Cena would win, they were almost certain. In the moments after it happened people claimed that it was a mistake that Sheamus won, and that another outcome was intended. Highly unlikely, as Sheamus celebrated rather than looked confused. For that reason, I think it's the biggest upset I can remember.
http://forums.wrestlezone.com/showthread.php?t=82551
As you can see, of the 21 predictions, 20 are for John Cena. More to the point though, almost everyone gave him maximum points, whereas the person picking Sheamus only scored it with the lowest value. In short, not only did people think Cena would win, they were almost certain. In the moments after it happened people claimed that it was a mistake that Sheamus won, and that another outcome was intended. Highly unlikely, as Sheamus celebrated rather than looked confused. For that reason, I think it's the biggest upset I can remember.