IT’S around 3pm on Saturday. My partner, friend and I are on a train from Essex to London. Eight young women are celebrating a birthday. They’re exchanging gifts, sipping canned cocktails and chirruping about the day ahead. Our friend is dozing, my partner and I chewing over the details of a film we recently saw. Occasionally a detail overspills the animated chat across the aisle and prompts a smile. They’re having a good day and we graze on it when we can.

“I need to see your IDs.”

It’s loud, authoritative. Our friend stirs. We shift on the scratchy moquette, look around. It sounds serious. I can’t help but feel a bit on edge. There’s no guard. So who’s asking?

It comes again. Not a question. A command. Insistent in volume, insistent in tone. The whole carriage is looking now. It’s the blonde man. The one in the blue T-shirt and grey hoodie from the other side of the cabin. I recognise him from my vague inventory. He’s among them now, going from one woman to another, waving some sort of ID pass. Plain clothes? Off duty? What’s the deal?

They’re ferreting around in pockets and bags, “we’re all 21”. They’re confused, but complying. Can they even challenge this? He continues to press them. Lurching closer to the women standing in the vestibule, muttering, pressing the questionable credentials into their space. Close enough to count his fillings, to feel the warm stain of his breath on their faces. He’s working his way round, taking in driving licenses, faces, names, addresses. Something isn’t right.

“Don’t give them to him. Don’t show him your details.”

We look on, sceptical. A woman speaks up and the details arrange themselves for sense-making. There’s an abandoned can of Stella minding his seat further up the carriage. The lanyard hanging from his hand, for a construction company. It makes sense. It’s a just a drunk dude bothering some women. Like the man on the Fife circle thumping my bike helmet hard enough to make me bite my tongue, or the old guy bluebottling around me on the last train from Glasgow, asking questions, getting closer, falling, bleeding on the floor, my bike, my shoes. The whole thing is unpleasant, for the women, for the rest of us. Conversations stop, eyebrows raise, questions start.

I asked my companions if they’d ever dealt with this kind of intrusive direction. The answer was predictably no. I was annoyed. I tried to game out the component parts with a gender flip. Could I imagine a lone woman doing this? Could I picture her mapping this out, crossing the carriage, interrupting young men, and ruining their day for fun? Could I imagine him approaching a group of young men like this? No.

There’s something especially pernicious about this sort of encounter. How often this – the intersection of power, sexism, public transport and cheap booze – actually happens. Every woman I know has a story about that drunk guy. It’s never entirely unexpected, especially at night. And all the worse if you’re on you’re own. It was kind of stunning to see it play out at a ratio of 1:8 in the middle of the day, with plenty of other people around.

He went back to his seat, laughing, revelling in his wit, pleased with his little victory. For the women, the happy chatter was over. Their conversation was now about him. He’d intruded on their day, imprinted on its memories, because it amused him and he could.

These days we’re having more discussions about this sort of behaviour, about the consequences of these seemingly minor disturbances, but we don’t talk enough about the selfishness of it. How even the smallest acts can change a day’s mood. How often women have to do the silent inventory when they travel, just in case. So often we’re told these things take on their ghastliness in our own heads, that they’re never as bad as we make them out to be. Often, the unpleasantness is explained away by those who didn’t witness it. It was hugely affirming to see my companions take it seriously, to understand the impact.

Watching men challenge moments of everyday sexism gives me hope. As did seeing the station staff listen and report it, knowing the British Transport Police would follow it up. Given how many encounters like this I’ve had during my life so far, it was a welcome change to see the safety of women quickly prioritised.

Women have spent so long challenging sexism largely alone that our words can blend into the background, lost to a feminist noise filter. When men challenge sexism in other men, things happen. A power bubble is more easily burst, with the potential to leave a lasting imprint on behaviour.

So to all the men who do it — thank you. And please keep speaking up. You can make a difference.