I hate to quantify the last decade as "the worst since ... x," because, frankly, the '80s had their fair share of problems, as did the '70s (Vietnam comes to mind), and the '30s weren't so hot either (don't get me started on 1140s ...)
But - the last 10 years really, really sucked.
We started with the millennium, and the Y2K bug. Not only did we kick the decade off with an expected, scheduled, Apocalypse, but it didn't even happen, setting the stage for 10 years of let-downs and anti-climaxes.
The worst of which was the 2000 election, where, after 2 long years of campaigning between Al Gore and George W. Bush (both candidates had been "shoe-ins" for their respective parties since around 1997 ... ugh), the nation went to bed on November 7, 2000 with no idea who had won.
What a disappointment!
All I wanted was for that damn election to be over. I'd waited months for mercy, and was denied for another month, with the official results, and George W. Bush's subsequent speech not arriving until December 13 ... over one month later!
The media totally "jumped the shark" that night (Nov 7), first calling the election for Gore, then Bush, then ?!WTF?!
September 11, 2001 was definitely the shittiest day of shitty, shit decade. 3,000 Americans died, and the rest of us suffered the mental scars of having such horrific scenes burned straight on to our retinas forever. To add insult to injury, the nation is still divided to this day over 9/11 with sad survivors bickering over who was to blame. I can't look.
This was also the decade that rock music finally died. Rest in Peace. I love hop-hop and pop music, but there really hasn't been a popular rock movement in this country since 1999.
The whole Bush presidency sucked. We've been embroiled in two endless invasions (Iraq, Afghanistan) for nearly 10 years now, and the infrastructure of the US has suffered immeasurably as a result.
2005: Katrina sucked ass. Not only did Mother Nature kick our asses, but the governmental (local, state, federal, etc.) response to this crisis was the real tragedy. This was the saddest spectacle of all because a lot of the hardships of Katrina's aftermath (still on-going, by the way) could have easily been avoided. I'll never forget FEMA saying they didn't know there were people in Convention Center, when any one who had watched any CNN that week knew about it.