我的微笑比不上她的呻吟
[wŏ de wēi xiào bĭ bù shàng tā de shēn yín]
Translating directly as 'My smile can't match her moan,' it suggests an ironic comparison between one's happiness (smile) and another’s expressions of pleasure (often sexual). It could imply that what gives him joy isn't as strong or valuable compared to his partner's experience.