拍马屁 pāimăpì Kiss Up to Someone

wher does it originate from?
As early as the Yuan Dynasty, herders were proud of raising horses. When horse herders encountered one another, they would often pat the buttocks of the others' horse and say, "What a good horse!" to fawn on the owner of the horse. At first, people only praised truly good horses, but soon people began to do this to flatter others, regardless of whether the herder's horse was good or bad, strong or weak. In this way, people began to flatter and kiss up to one another, and this action became known as 拍马屁(pāimăpì) to kiss up.

What does it mean?
拍马屁(pāimăpì) refers literally to patting a horse's buttocks: 拍(pāi) means to pat; 马(mă) is horse and 屁(pì) refers to fart or buttocks. But now 拍马屁(pāimăpì) is widely used as an analogy to ridicule blatant flattery that is meant to please others without regard for objective reality. Consequently, people who like to kiss up or brownnose are called 马屁精(măpìjīng), which means flatterer or brownnoser.

wher is it used?
拍马屁(pāimăpì) is usually used in the following context:
e.g. 这家伙是拍马屁的好手，总能让上司高兴！  
       Zhè jiāhuo shì pāimăpì de háoshŏu, zŏng néng ràng shàngsī gāoxìng!
       This guy is an expert at kissing up, always pleasing his authorities.
       他善于拍马屁，所以升迁很快。  
       Tā shànyú pāimăpì, suŏyĭ shēngqiān hĕn kuài.
       He is good at kissing up, so he gets promoted very quickly.