I think it is different if other peoples kids are in your home – they tend to be more respectful, all I have had to say in the past is “if you do that again/if you even think about doing that”, “I will tell your mum/dad” – that did the trick! :D
As for out and about, I did jump in between a guy and presumeably his g/f, and got a shiner to prove it – not going to do that again, but, I have rung the police since if I see a scene escalating.
On the other hand – when my son was about three and a half he opened a door for two old ladies – neither of which said thank you – he wondered why they were so rude – I went up to them and gave them a right stripping down, I can tell you!