If you just warn people, they often simply ignore you. But if you ask them a question, then they have to think about it. And once they start to think about the consequences, they almost always calm down. Unless they're drunk, of course. Or stoned. Or aged between fourteen and twenty-one. Or Glaswegian.
Ben Aaronovitch...don't ask me why I know what an Edwardian smoking jacket looks like: let's just say it has something to do with Doctor Who and leave it at that.
Ben Aaronovitch