yank (someone's) chain
to tell a lie (and have somebody believe it) for a joke

– examples:

“No, no, don’t call her. I was just yanking your chain. She isn’t really on a date with her ex-boyfriend”

yellow streak
(also: ‘(be) yellow bellied’)
to be a coward; to be prone to cowardice

– examples

He is a nice guy, but with a terrible yellow streak. Whenever his friends are in trouble, he runs away.

yes man
a person who always agrees so that the other person will like them more (usually a member of staff always agreeing with a boss)

– examples

“Tell me what you really think. I don’t need a bunch of yes men around me.” [/

you can say that again
(spoken as a response)
Equal to ‘I totally agree’; ‘what you said is exactly right’

– examples

“Dave is such a womaniser.”
“You can say that again; I saw him flirting with his girlfriend’s mum last week.”

you can't make an omelette without breaking eggs
to make progress, some people have to get hurt or some things have to get broken

– examples

Dave has made millions, but now his old school friends all hate him, saying that he used them. He doesn’t care, saying that you can’t make an omelette without breaking some eggs. [

you can't take it with you
use it now, because it will be useless to you after you die (often talking about spending money)

– examples

His parents are spending all their money now that they have retired. He can’t blame them – you can’t it with you – but it would be nice, he thinks, if they leave a little for him.

you get what you pay for
if you spend only a little money, you get a bad product; if you spend more, you get a higher quality

– examples

I bought this pepper grinder last week from the dollar shop, but it has already broken. I suppose you get what you pay for; I’ll get a better one next time.

young blood
young people with fresh ideas

– examples

“The boss says that the company’s ideas are tired, and we need some young blood to freshen the place up. I think, however, experience is important.”