The Wanted -- Karaoke + Beer = Goo Goo Dolls

Breakout British boy band The Wanted has violated the ONE rule of alcohol-fueled karaoke night -- YOU CAN'T ACTUALLY BE GOOD AT SINGING ... and TMZ has the video proof.

It all went down at Rock & Reilly's Monday night in Hollywood ... the boy band -- known for their new hit "Glad You Came" -- grabbed the karaoke mic and belted out the 90s classic song "Iris" by the Goo Goo Dolls ... and damnit ... it was way too good.