对你微笑纯粹出于礼貌
[duì nĭ wēi xiào chún cuì chū yú lĭ mào]
Translates literally into 'my smiling at you is solely out of politeness'. It could suggest keeping emotional distance without revealing true intentions or thoughts, only maintaining a friendly surface interaction with the smile meant merely formal courtesy rather than genuine friendliness toward the addressed person(s).