People often ask why music power couple Gavin Rossdale and Gwen Stefani don't perform together. The following video is the answer to that question.

Gwen Stefani has a unique voice and is no stranger to unorthodox collaborations -- her duet with the late Bradley Nowell on 'Saw Red' comes to mind. Where that track succeeds, her latest collabo with husband Gavin Rossdale and Bush does not.

Not too long ago, Rossdale said that the likelihood of the couple recording together was not very high. The audience at KROQ's Almost Acoustic Christmas found out why on Saturday (December 8th) during Bush's performance -- because their voices mix about as well as oil and water.

Gwen jumped on stage during what is arguably the band's most well known track, 'Glycerine.' Let's just say that her sporadic vocal style doesn't really match up with that of the song or her husband's voice. As much as we hate to do it to a band we like, we have to stamp this one as a Rock Fail. Check out what is probably (and hopefully) the last Stefani/Rossdale duet below.