1.
to always have a comeback; to be quick-tongued; to never be at a loss for words
Describes someone who always has something to say in response, especially excuses or cheeky replies. Usually said with mild exasperation or disapproval about someone who talks back no matter what.
I'm having trouble with a child who always has a comeback no matter how much I scold them.
Usage
An idiomatic expression with a negative connotation. Used when someone is being criticized or confronted but keeps talking back instead of accepting the criticism. The literal meaning is 'the mouth doesn't decrease' — i.e., they never run out of words.