想大笑最终却只能扯扯嘴
[xiăng dà xiào zuì zhōng què zhĭ néng chĕ chĕ zuĭ]
A more colloquial translation could be 'Wanted to laugh loudly but ended up only grinning'. It indicates a sense of inner struggle, trying to be happy but unable to completely let loose, probably under certain external pressures, which result only in a bitter smile.