带着绿帽子的小白脸
[dài zhe lǜ mào zi de xiăo bái liăn]
'Wearing a green hat' is a euphemism for someone whose partner is unfaithful. '小白脸' ('xiǎo báilǐan') usually refers to a good-looking young man, sometimes with connotations of weakness or dependence. Altogether it humorously or sarcastically refers to someone being cuckolded yet remaining physically handsome.