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.


The lyrics include, quote, "Oh you know females and how they run their mouths . . . They try to get at me / Behind your back / Tryin' to tell me that I'm just like the others / But I ain't all bad."


He also re-Tweeted a fan who said, quote, "I think Justin was shading Taylor Swift in #AllBad."