笑衬心寒
[xiào chèn xīn hán]
A seemingly paradoxical combination of 'a smile' ('笑' - Xiao) and 'a chilled heart' ('心寒' – Xin Han). It conveys a sense that, beneath apparent joy or amiability (symbolized by 'smiling'), one's true inner emotions or thoughts may be very cold, indifferent, unhappy, or even depressed.