WE'RE ACTUALLY NOT SURE WHAT THIS SMELLS LIKE

At manager Adam Leber's 40th birthday throwdown this weekend in L.A., Miley Cyrus joined the karaoke band for a no-holds-barred rendition of "Smells Like Teen Spirit," featuring diminutive guest vocalist Donnie and SONGS President Ron Perry on guitar.

Miley, who is expected to drop new music soon, said in a recent interview that she's taken a hiatus from weed. Donnie, however, handed Ron a blunt that inspired the publishing exec to bust out a medley of heartrending ukulele ballads.