Although we're only colleagues, he's very polite to me and keeps his distance.
Tips
usage
不客气 is the standard "you're welcome" in response to 谢谢. 别客气 means "don't be so formal / polite"; used to put someone at ease.
culture
Being told 别客气 is very common in Chinese hospitality. Hosts expect guests to be 客气 (humble, politely declining offers at first), and then hosts insist. It is a social ritual.
