Public transport, and the way people behave on it, tells you a lot about a city. I once asked a teenager on the London Tube if she wouldn’t mind picking up remains of a sandwich she’d tossed on the seat next to her, mayonnaise and limp lettuce oozing onto the blue and red fabric. “Mind your own f****** business,” she shouted at me. Trying to keep calm, I carried on, explaining it was “everyone’s business” to keep the Tube clean because it’s a public space we all use.