get on (one's) case
get on (one's) case
To start bothering someone about something. Oh, don't worry—I'll get on Pat's case until he agrees to go to the interview. It's too good an opportunity to pass up.
get on someone’s case
in. to start harassing someone about a personal problem; to annoy someone. (Compare this with get off someone’s case.) I’ll get on Tom’s case about being late so much.