Green Day frontman Billie Joe Armstrong is checking himself into rehab after a rant mentioning Justin Bieber last week in Vegas. Armstrong ended the band's performance at the iHeart Radio Festival after an obscenity-laced tirade, smashing his guitar, then storming off stage. "I'm not effing Justin Bieber," Armstrong screamed after he thought he had been told to wrap up the set, according to MTV. "Green Day wants to apologize to those they offended," reads a statement on the band's website. "We regretfully must postpone some of our upcoming promotional appearances." What substances Armstrong has been abusing were not revealed.