没哭没闹就是忘了怎么笑
[méi kū méi nào jiù shì wàng le zĕn me xiào]
Says, 'I didn't cry, I didn't make a fuss, I just forgot how to smile'. This expresses inner sadness; instead of expressing emotions outwardly through crying or complaining, they feel so upset and helpless internally they even forget what makes them happy and they can't bring themselves to smile.