。
My boss works us like a slave driver.
Literal
I [of-の] boss [topic-は] employee-handling [subject-が] rough is [explanatory-んだ].
人使いが荒い is a set expression — 人使い ('handling workers, treating employees') + 荒い ('rough, wild'). Literally 'rough handling of workers' = 'a slave driver, hard on employees.' A classic workplace complaint. The んだ frames the statement as venting.