sing off-key
sing out of tune

He's arrogant, irresponsible and crude, and, in addition, sings off-key.

The way your smile just beams, the way you sing off-key.

Taylor Swift sings totally off-key, especially live.

And this is hardly the first time she has sung off-key, as a gag, publicly.

It has a soft reedy voice and it sings slightly off-key.

Curtis raised a clenched fist and sang off-key.

The cast members, though usually at least two decades older than their characters, aren't afraid to whine, giggle or sing off-key.

"He's killing the song," Biolay told me as the old man sang off-key.

'Too hot not to cool down,"' he sang off-key.

He deliberately sings off-key and often high-pitched, so has a recognisable voice.