be on someone's case

be on (one's) case

To be constantly nagging, harassing, or annoying someone. My boss has been on my case all week to get that report done. I'm sorry for being on your case about it, but I need an answer soon.
See also: case, on

be on someone's case

INFORMAL
If someone is on your case, they keep criticizing you or telling you that you should do something. Note: In the first two expressions, a case is a matter that is being dealt with by a lawyer or doctor, rather than referring to a box or suitcase. My parents are on my case night and day because they say I'm not studying enough. Note: You can also say that someone is getting on your case. I just didn't want Joanie getting on my case as well as everyone else. Note: If someone tells you to get off their case, they are telling you in an impolite way to stop criticizing them. Get off my case, will you?
See also: case, on

be on (or get off) someone's case

start (or stop) criticizing or hounding someone. informal
See also: case, on