Well, Bee, I'd encourage him.
To try singing it sober, of course. It's not bad as one's only party piece.

But then, I'm known to be odd, especially in my belief that most people who "cannot sing" are usually that way because that's what they were 'taught'; I wouldn't accuse 'catters of such behaviour. I suspect a few errors of pitch wouldn't do the song any irrrevocable harm and may actually improve its delivery in some circumstances.

Cheers, Rowan