1. In conversation, to someone who’s just expressed an opinion you viscerally disagree with.
2. In an argument.
3. At the start of a sentence.
4. On a plane, to the parent of an awful child.
5. On a train, to somebody who has just mashed your face with his backpack.
6. To someone who just put a divider between their shopping and your shopping at the checkout.
7. On the radio.
8. In a country lane, to the prick in a Range Rover who forced you to reverse 200 yards so he could pass.
9. In a leaving card.
10. In parliament.
For those not currently addressing the House, just shouting WURRRH is also acceptable.
11. In an email.
12. To a hairdresser whose appalling work has left you on the verge of tears.
13. In a black cab.
(This must only be done after two minutes of pregnant silence).
14. On a zebra crossing, to the man who wasn’t going to stop for you.
15. At a bar, to someone trying to get served before you.
16. To someone on the pavement with a clipboard and bib.
17. In a queue, to somebody who just cut in.
18. In countries where it is customary to tip.
Images via Shutterstock.
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