i-adjective
prone to complaining; grumpy; querulous
Describes a person or their manner as habitually complaining, whiny, or irritable. Often used for someone who frequently voices dissatisfaction.
彼は最近愚痴っぽくなっている。
He has become prone to complaining lately.
愚痴っぽい口調で話すのはやめてください。
Please stop speaking in a querulous tone.