It's official: Multitudes are sick of Bieber fever. At the Billboard Music Awards, held in Las Vegas on May 19, the feisty crowd booed Justin Bieber as he accepted the fan-voted Milestone award; the 19-year-old beat out the likes of Bruno Mars and Taylor Swift for the honor. ''This is not a gimmick,'' Bieber whose music has been overshadowed recently by his love life, partying, and pet monkey said from the stage. ''I'm an artist and I should be taken seriously.'' Even Swift the night's big winner, with eight awards seemed to be drinking the haterade: She was taped playfully sticking her tongue out when BFF Selena Gomez kissed on-again boyfriend Biebs. The headline-generating show (which also featured Miguel accidentally jumping on an audience member) sparked much debate on Twitter, where Bieber, Billboard's Top Social Artist winner, is a key figure. From May 19 to 20, he inspired 300,000 negative tweets and 1.6 million positive ones, says social-analytics company Topsy. Among his supporters? Chris Brown, who tweeted (and apparently later deleted) ''Love ya boy!'' And there's a man who knows about backlashes.