Last night, the Canadian industry savior and haircut titan Justin Bieber overcame a cold and a guest appearance from Sean Kingston to sell out Madison Square Garden. The performance was being taped for an upcoming 3D biopic, and thus Bieber brought out the big guns: Boyz II Men. (Usher, Jaden Smith, and Ludacris were also in the building.) But the evening's reported highlight? A duet with 17-year-old Miley Cyrus, who just happened to have separated from her boyfriend last week. Together, they sang "Overboard," a song Bieber initially recorded with his opening act, Jessica Jarrell. At the time, the substitution of Cyrus for Jarrell seems to have played well with the crowd--listen to those screams!--but Bieber nation is a notoriously protective bunch (see: Kim Kardashian), and the backlash against Cyrus online was swift, immediate, and fearsome. Watch your back, Miley: