Expressions used in Everyday Spoken English in Social and Professional contexts
If you are 'on someone's case' it means to frequently criticise them and their actions behaviours or habits. If someone is continually monitoring you or commenting on what you are doing you can tell them to 'get off my case', which is another way of asking someone to 'leave you alone'. This is a very informal expression usually used with people you know very well or in social situations. Telling someone to 'get off your case' might be insulting in the wrong context.