苦人心
[kŭ rén xīn]
This nickname reflects the person who might have had a rough experience in life or has some heavy mental burdens or worries. The word expresses a sentiment of pain in heart which indicates the inner sufferings the individual goes through. 'Kuxinren', directly translating to bitter one, implies a state that life is filled with hardships and challenges and sometimes, there's bitterness inside one's soul.