to say or do no more about something.

I've simply decided to quit – let's leave it at that.

• be a hard act to follow
• be ahead of the game
• be ahead of the pack
• be a ... in the making
• be a laugh a minute
• be a law unto
• be a law unto yourself
• be a licence to print money
• be alive and kicking
• be alive and well
• be alive with
• be alive with something
• be-all and end-all
• be all beer and skittles
• be all brawn and no brains
• be all dressed up and nowhere to go
• be all dressed up with nowhere to go
• be all ears
• be all eyes
• be all fingers and thumbs
• be all fun and games
• be all heart
• be all in
• be all in a day's work
• be all in mind