I have seen posts on TMC before about problems like you describe. I'm not going to make a judgement about who was "rude", it doesn't matter, I am simply going to offer a possible solution.
When you are charging in a situation like you describe, at a publicly available J1772, on a piece of paper write your name, cell #, the time you started charging, and state that you will be checking your Tesla app to determine when your car is done charging and at that time you will come unplug your car, or they can call/text your cell and ask if they can unplug you to charge their EV. Tape the piece of paper next to your charge port.
This assumes of course that there is cell service at the charger site and wherever you are located while your car is charging.
Obviously a selfish person could ignore your note and unplug you and start charging their EV. Since the Tesla J1772 adaptor does not lock itself to the charging cable you cannot prevent someone doing that. If you have cell service you can monitor the charging state of your car.
So all I am suggesting is some common sense and common courtesy could solve the problem you describe.
Such situations are why I try to avoid public J1772 chargers, but sometimes they are needed.