Arcade Fire were never a band I enjoyed, but I acknowledge they made some different sounding music. As for worst band of the decade, a lot of stuff comes to mind. I absolutely despised My Chemical Romance, if any remembers them. Who can forget the Pussycat Dolls? Tokio Hotel, Soulja Boy, there's so many.
And speaking of Nickelback, they may not have been from this decade but this is hilarious:
I've never been to a concert where the band asks if they've got any fans and no one cheers.