A man was hit by a car in the middle of a busy street. A large crowd gathered, drivers pulled over, people stared down from their balconies. But it was a full ten minutes before anyone called an ambulance: everyone assumed someone else had done it. This tale, or variations on it, is drummed into every schoolchild in America. Growing up in the US I was often reminded that it was my civic duty to look out for the common good. There should be no hesitation in taking matters into your own hands: we are all citizens on patrol – in fact, the origin of the word cops.

This attitude extends from life-saving to the seemingly mundane, which is probably why I receive strange looks in Britain. On the bus, adolescents and adults alike stretch out, feet propped up on the seats as if they were at home in front of the telly. I am too incensed to feel fear or intimidation: whether it’s a large, inebriated man or a cocky teenager, I tell them to put their feet down. I ask if they would like to sit where my filthy feet were once lying, and nine times out of ten they sheepishly comply.

When not preaching to the feet slobs on public transport, I’m on my soapbox in London’s parks. Despite acres of lawn and footpaths, parents and dog-owners seem to feel compelled to allow their children and animals to run wild on the cycle lanes. Often my admonishments are greeted by protests from people that their cherubs and precious pets should be allowed to play wherever they like. I remind them that should their child or animal get maimed while playing on the designated cycle paths, they have only themselves to blame.

And although I am often reminded that we drive on the wrong side in the US, at least we know to walk on the “right” side. On countless occasions I’ve been walking up the left side of an escalator when someone near the top tires and decides to stop. Instead of moving to the right, they block the rest of us. While the Brits around me fume under their breaths, without hesitating I bellow “Stand to the right, walk to the left”, and get our line moving again. Despite the quizzical stares, there is a palpable sense of relief and silent gratitude. It’s not that I’m fearless, it’s just that I tell myself: if I don’t say something, who will?

Times recommends

• Live chat: Thrifty ways to update your winter wardrobe
• Is anybody out there really listening?
• Nutrition Q&A: Will eating late make me fat?