你笑起来真的好看对你微笑纯属礼貌
[nĭ xiào qĭ lái zhēn de hăo kàn duì nĭ wēi xiào chún shŭ lĭ mào]
'Your smile is truly beautiful, but I smile back just out of politeness' expresses a mixed feeling where someone acknowledges another person's attractiveness but maintains distance and decorum.