JUSTIN BIEBER dropped a new song yesterday called "All Bad" . . . and it sounds like it's an attack on TAYLOR SWIFT, who's been critical of Justin since becoming friends with his ex SELENA GOMEZ. In the lyrics he's complaining about how some girls try to sabotage his game by telling other girls he's a bad guy. He also re-Tweeted a fan who said, quote, "I think Justin was shading Taylor Swift in #AllBad."