Harriet Walker: A hairy armpit? At a birthday party? You're under a vest

Sleep on the left side, goes the adage, to keep your sword arm free. It speaks of ancient and arcane times when a bloke could be ambushed in his hut wearing only a loincloth. These days, the motto for the modern man seems to be, "Put a vest on and you'll be able to throw punches more easily."

Last weekend saw my second social event in as many months disrupted by men wearing vests; the first was my own birthday party. The interlopers, highly conspicuous by their lack of sleeves, jabbed a guest in the throat before you could say Bruce Willis.

The confluence of vests, virility and violence is a baffling social logarithm. On the one hand, they're mostly worn by aggressive, portly, tattooed men who don't feel the need to hide their bingo wings. On the other, lightweight vests of the skinny variety are currently beloved by boy bands and hipsters the world over.

Which brings me to the second incident, at a housewarming, when a trendy-wendy in a skinny scoop-neck vest punched a man carrying a handbag in the face. He even took his plaid shirt off to do it – you can imagine the middle-class horror. "Put your shirt on," cried his friend, "you're not Hulk Hogan."

This, of course, is the source of the vest's power: the rough and ready athleticism of the wrestling arena. Cage fighters and their ilk wouldn't be seen dead in a sleeve, and male vest-wearers covet their gravitas.

I, however, remain convinced that all that rugged machismo is choreographed to within an inch of its life; it's not natural to fight back after being hit with a chair.

Vests work in this context, though, because wrestlers and fighters are as hairless as newborns. When I say there's something obscene about men in vests, I'm not affecting that fashion hyperbole which is offended by ugly skirts and horrified at imperfection: I mean simply that the sight of a nestling clump of matted armpit hair is acceptable only in the bedroom or on the basketball court. Certainly not on someone's birthday.

But you need muscles too, because all those ultra-cool wimpsters who wear their vests with jackboots rather than high-tops end up looking a little like Dickensian orphans. The catwalks of Rick Owens and Hedi Slimane (he who brought skinny chic to Dior Homme) are really the only place these waifs can exist peacefully in a vest.

Of course, the ideal scenario is a woman wearing it. A well-chosen jersey vest is perfect for layering this time of year. Helmut Lang, Rick Owens (him again!) and Damir Doma exemplify the minimal, restrained placidity of the feminine vest. Just don't get in a fight if there's only one left in the shop.