get a bum rap直译过来就是：“被粗劣地敲了一下”，这个短语的正确意思是：“受到责骂、责备，受到不公平的判决”。因此，当美国人说"He got a bum rap for taking sides with his subordinate."时，他/她要表达的意思就是:"He was blamed for being partial to his subordinate."、"He was criticized for taking part with his subordinate."。
Benjamin: The financial executive has been in a bad mood since he came out from the meeting room this morning. How come?
Terry: He got a bum rap for taking sides with his subordinate.
①We'd better not give him such a bad earnings report while he is in such a bad mood.
②And he even got a severe punishment.
③The manager criticized him to all staff's beard at the meeting.
④Why? He simply stated the fact.
1. partial adj. 偏爱的，偏袒的
He's partial to sporty women with blue eyes.
I might be accused of being partial.
A newspaper criticized the president's proposal, saying that it was partial to Israel.
2. take part with 支持，站在一边，袒护
He always takes part with his brother.
You always take part with the unscrupulous man.