expression, noun-modifying (irregular)
fast-talking; never at a loss for words; always ready with a retort
Describes a person who talks back readily, argues persistently, or always has a quick reply; often carries a negative or critical tone. The expression is fixed and used prenominally, as in 口が減らない人 or 口が減らないやつ.
See also: 口の減らない
He's a fast-talking guy who always has an excuse ready.
Arguing with someone who never runs out of words gets you nowhere.