After meat, mustard phrase
Used to imply that something has come too late and it is no longer needed
He quits smoking after knowing that he got lung cancer. After meat, custard.
A: "I'm bringing my drill to you." B: "Ah, after meat, mustard. I've borrowed it from a neighbor."
To do something or go somewhere very quickly, usually because you are about to be late or you are late
The idea of the idiom may come from the fact that you do not need mustard when meat has already been eaten.