I would do nothing and it wouldn't bother me in the slightest. Hair is only anathema to me if it's
d i r t y. (however . . Himself would look beyond ridiculous with that particular style! Bahahaha!) When I was a kid that style would have indicated a Teddy Boy or a Spiv. We also had Mods and Rockers. Jeez, I'm old.
Well, after I recovered from my jaw dropping to the ground, and stopped laughing after about a week, I would march him right back to the hairdressers , and ask him if he had been temporarily insane !!!!
I'd ask him how he regrew his hair! Hypothetically, if he had enough hair to do it well, it's his head, he can do what he likes. He'd never cut it like that though, it's not his thing. Just as well or we'd almost be matching (mine looks a bit like that at the moment, except that it's red).