抱大腿
bào dà tuǐ
The meaning of this phrase is to signify someone trying to curry favor with someone else.
However, if you break down the phrase, you will realise that it is not what it means if you directly translate it:
抱: to hug
大腿: thighs
Therefore, the direct translation of the phrase is "to hug (someone's) big thighs"
This reason why the act of hugging someone's thighs was translated to mean to curry favor with someone was because it originated from people who were buddhist and praying to buddha for help. The statue of buddha in temples are usually huge and so people will 'hug' his thighs/legs when praying for help.