Often when people say, " I hope you don't mind", (usually with a big smile on their face) they know that they are out of line. They are trying to embarrass you and pressure you with this, "I hope you don't mind" line so you don't confront them with their bad, irritating, or boundary busting behaviour. They expect you to say, "No, that's okay". Watch them looked shocked when you say, "Yes, I do mind".
For most people, when they say, "I hope you don't mind", they know full well that they are stepping on your toes.
Some people with weak boundaries say this and are apologetic, "I hope you don't mind if I take my lunch break", when they have the right to take it. This is a different story. In this case you say, "Of course I don't mind". These people need reassurance.