Also in English culture, though few remember it any more. In Shakespeare’s time, though, it was clear what it meant for a man to wear horns. I wouldn’t be surprised if the concept were German, too.
Another reason why horns or wings on a helmet is a dumb idea: cock your arm back like you were going to chop overhand with a sword (or throw a football)… those horns would certainly limit the range of motion, or maybe get things tangled up. You might be the coolest looking Viking at the battle, but I don’t think you’d be the most effective…
The real problem with horns and such in battle is that when the other guy’s sword comes swinging down towards your helmet, it will catch the horn and knock the helmet off, not good. The standard conical-rounded helmets of the time were shaped precisely that way to defend against such swings. You want the other guy’s sword to deflect a little sideways away from your head. Smooth is good, protrusions are bad.
Unless there’s a chin strap on the helmet. And wouldn’t this be preferable to a glancing blow on the head? The sword will be deflected onto your shoulder, possibly chopping your arm off. I think I read somwhere that this is the reason for the protrusions on Japanese armor, i.e. to stop the sword at the helmet rather than allowing it to swing down further.
I included an obscure cuckolding pun in an early draft of the report but thought better of it. I never considered it in relation to Hunding, but it does fit. I suspect Wagner et al. intended it as theatrical shorthand to indicate primitiveness more than anything else.