"It's none of your business" is an everyday expression used to convey to the person being addressed that the matter being discussed (could be about a person) is no concern of that person & he/should not interfere in the matter or try to find out more about it.
The expression "It's none of your business" is most often said in an angry tone of voice, perhaps with pointing fingers or banging the desk to emphasize the point. It may even be said like this: "Damn it! It's none of your business!" or "What the hell! It's none of your business!" or "Get lost! It's none of your business!"
Note: The exclamation mark gets conveyed in the conversation through the loud tone of voice.
1. Sharad got angry when his mother repeatedly asked him why he came home so late in the evenings when his college got over by afternoon. He very rudely shouted "It's none of your business where I go after college".
2. When the executive started asking probing questions about the new project, the boss sternly admonished him saying "It's none of your business. Just do the work you have been given."
3. The Police Commissioner summoned Prakash and told him that as he had been suspended, he should no longer investigate the forgery case. When Prakash started arguing about it, saying he could find clues, the Police Commissioner told him, "This is your last warning. It's none of your business any more and you had better stop your investigations."