Idiom for the Day

'The Bee's Knees'.

'Have you tried the new pizzeria, it's the bees knees?'.

You can use 'to be' + the bees knees to describe something outstanding or excellent.

The origin of the expression 'the bees knees' is thought to have come from 1920s USA, although no one seems to know how it developed. Like many expressions in English it appeals to speakers and listeners because the words rhyme. 

It is similar to other expressions which have the same meaning- the cat's whiskers or the monkey's eyebrows.  

A cruder version of this is: it's the dog's bollocks (testicles). This can also be used to be disparaging about someone who has a high opinion of themselves- 'He thinks he's the dogs bollocks but...'

This expression has been changed to make it rhyme into: It's the mutt's (a slang name for 'dog') nuts.

Non-native speakers of English need to be careful using idioms because it is easy to make mistakes, or to use them inappropriately. Also idioms come in and out of fashion and so what sounds cool one day can sound silly another.

'The bee's knees' is used today and can be used in most situations when you want to describe something you really like or enjoy,

Thanks to: Fernanda Povoas for the suggestion.