Understand English Humour – Onion Skin

Learn British English idioms, phrases, expressions, and vocabulary, and improve your British English pronunciation and English accent with an experienced and innovative native British English teacher.
An onion walks into a bar.
Onion: "A pint of your very best Britlish bitter, my good man, and a glass of white wine for my wife."
Barman: "I'm sorry, sir, but we don't serve food in here."
Why is this funny?
It's funny because of the ambiguity in the term serve food.
In many UK pubs you can order drinks, like beer, and food to eat with it.
To serve means to sell or provide someone with something.
Many pubs serve both food and drinks.
Some pubs, however, don't sell, or serve, food. They only sell, or serve, alcoholic drinks.
An onion is a type of food.
When the barman says, "we don't serve food", it could also be taken to mean, "we don't serve a certain type of customer."
Notice the pronunciation of the word onion / ˈʌn.jən /. Many students mispronounce it.
If you know your onions, you won't mispronounce it.