across the board
it applies to everyone. Everyone will have to do it, or everyone will be affected by it.

– examples

We have some new rules, and these apply across the board, so the teachers will have to follow them too.

After the terrible year last year, they made changes across the board.

acid test
The conclusive test that will prove if it is good or not.

– examples

The numbers work in theory, but the acid test will be when the product goes on the market.

They are top of the league after half a season, but the acid test will be April when they play away to Manchester United, Barcelona, Brazil and Aberdeen. Then we will know how good they are.

The company is looking good now, but the acid test will be what happens when the market goes down and consumers don’t want to spend so much; if they can still make money then, then their future looks bright.

a little bird told me
I heard from someone (but I’m not going to tell you who)

– examples

A little bird told me that you’ve been dating Dave. Are you sure that is a good idea?

A little bird told me that things aren’t going well at your company. Maybe we can talk about transferring you to ours.