Humanity still didn't learn a blinking thing amidst their increasingly vast stupidity.
-Biggest disappointment.
Agreed. Also on the list:
Humanity not answering the questions I have asked it.
Humanity failing to recognize the ambiguous responsibilities I have set forth upon it.
Humanity having too much fun at a party doing jello shots off that total slut.
Say what you want, but this decade was fine. Someday, you're going to be looking back at this decade from the future, and you're going to say, "HA HA, THOSE WERE THE DAYS" even if you enjoyed it as much as the sentient cancer you got from that new pair of telepathic emitters your adopted alien son gave you for the annual MySpaceBarBrokeian Festivals that will have taken place after I singlehandedly fought off entire hordes of Space-Nazis.
...I seem to have lost my train of thought. In any case, hindsight is 20/20, and that is definitely something we can rely on.
I'd say sexual predators are the biggest disappointment of the decade. Come on, sex offenders, what have you become? You used to be feared like nobody's business! Parents warned their children so much to beware of strangers, and worried the hell out of Trick-Or-Treating. Now look at yourself! Look what you've accomplished in the past few years. You got caught through conversations on AIM. You end up on social networking sites posing as teenagers. Chris-Fucking-Hansen from Dateline has become your archnemesis! And to what end, ass bandits? You're marked for life. Forever you shall be listed as registered sex offenders, the location of whom I can easily look up online.
In honor of this once revered group of criminals, I propose that the 2000's not be called the aughts, or the zeroes, but the Ped00's.