Amen.
How much could it hurt to approach the problem from another tack eg.
"couldn't help but notice you're shifting a lot of air, do you mind if I make a couple of suggestions? In my experience a couple of small changes can make a big difference." helpful, polite etc. the suggestion is not rammed down the embarrassed divers' throats.
sounds a lot better than
"now I'll teach you how to breathe like a scuba diver" (I paraphrase, but that's how it would come across to me) how patronising is that?
No sensible diver's going to say no, but if you've got some idiot who thinks he's good enough and won't listen to advice, then you point out that his inability to dive well is affecting the rest of the group.
Cheers,