the dirty work直译过来就是：“脏活儿”，这个短语的正确意思是：“吃力不讨好的活儿”。因此，当美国人说"He did the dirty work on that project."时，他/她要表达的意思就是:"The work he did on that project was arduous but unrewarding."、"It is really a thankless task that he did on that project."。
Shirley: I hear their project is totally a success. So how much bonus could Terry get this time?
Benjamin: Oh, don't mention it. He did the dirty work on that project.
①I am sorry to hear that.
②Did he just accept it?
③I think he has the talent to do more important work.
④The supervisor is really bad to him.
1. unrewarding adj. 无报酬的
Listening to it in its entirety is also fairly unrewarding.
Markets today would not tolerate unrewarding and risky investment on this scale.
Lectures often seem very formal and empty things; recitations generally prove very dull and unrewarding.
2. supervisor n. 主管
Each student has a supervisor to advise on the writing of the dissertation.
A supervisor praised the employee for her good work.
My supervisor is a spineless person. He never stands behind his decisions.