This is a comeback/remark acronym that means "none of your
business". It can be modified and intensified by adding letters like "NOYDB" or "NOYFB" for "none of your damn
business" or "none of your
fucking business". These are used when you want to make it clear to someone that they have overstepped a line/boundary and you are not comfortable sharing particular information with them.
Person 1: When are you going to the party?
Person 2: NOYB.
Person 1: ok, sheesh, sorry I asked...
Person A: What's your address so I can see how far you live from me?
Person B: NOYFB!!!
Person A: K...
Person A1: How much
money do you make an hour?
Person B2: NOYDB......
Person A1: It is though, I help you with your taxes...
Person B2: Idfc