For years I’ve fumed silently at loud phone conversations on buses. I have planned horrible eviscerations, shopped online for signal jammers, and made jokes to my companion about there being nobody on the other end of the phone. I’ve tormented myself, reading the same sentence in my book over and over – most of the time not distracted by the noise itself, but by my frustrated rage. Then one day, not long ago, the penny dropped. A woman on the top deck of the bus was yelling into her phone. Her boss was an idiot and she’d had it out with him, she explained to her friend. “I told him that it wasn’t on and he didn’t know where to put himself,” she said. “I just looked at him and he backed right off.”

On the other side of the aisle, I went through my normal routine of rewriting the story in my head. “You mean he told you to do unpaid overtime and you said: ‘Ooh, thank you – how much?’” I grumbled silently. I sent a couple of death rays into the back of her head. They had no effect, as usual. The woman was settled, oblivious. The conversation was clearly going to last a long time, and even if I moved to the back of the bus it would still be audible. I was in hell, and I didn’t have any automatic weapons or an iPod on me. And then the fog cleared.

The effect was instant and extraordinary. ‘Oh, yes, I’m sorry,' she said, with a placatory answering smile

I walked up to her seat, smiled at her and said: “Excuse me, would you mind keeping it down a bit?” The effect was instant and extraordinary. “Oh, yes, I’m sorry,” she said, with a placatory answering smile. She lowered her voice markedly, and drew the conversation to a close soon after.

And there is the next problem. I got what I wanted, but I felt guilty that I’d ruined her day. I still feel that now. Last week I was in a coffee shop, reading. The young man next to me was talking on the phone; not loudly, he wasn’t bothering me. When his call ended he turned his phone sideways and started watching a video with the sound loudly broadcasting. This is where I drew my line in the demerara.

“Excuse me,” I said. He turned slowly to look at me. “Would you mind wearing headphones, please? It’s rather loud.” He grunted and turned the sound off. I read my book and he sat looking into space. Shortly afterwards he left, and I felt guilty again.

But most of the time it works wonderfully. Smiling at people really helps, though this perhaps isn’t something you should try with gangs of lairy blokes, or late at night. And if someone’s having a quick chat or struggling with technology, again it’s best left alone. Loud music - or sodcasting – is also beyond my remit.

The revelation has been that a lot of the people shouting on public transport aren’t doing it to ruin things for everyone else. Sometimes they just don’t know they’re making such a racket – or possibly they don’t think anyone cares – and a gentle reminder of our mutual humanity makes for a much more harmonious bus ride than seething resentment and isolating obliviousness. It’s scary to do sometimes, but it also feels much more human and connecting. It’s the secret power of telling off.

• Kay Holmes is a freelance journalist