You're the asshole in that situation. Don't expect that any parking place is yours until it's empty, especially when you have no idea when the people actually parked in the space are leaving. You should never be blocking traffic waiting to park in an occupied space because you assume they're leaving.

I understand this. At work parking is hella bad, so I routinely get to work over an hour early just for parking, and then most days I bring lunch or don't eat because I don't want to lose my parking during the day.

That being said, because I know parking sucks there, I'm extra quick when I do have to leave because I know the feeling of driving around looking for parking, becoming hopeless, and resigning to the quarter mile walk from the next closest available parking.

I've never understood the people who purposefully just sit there and stare at the person needing a parking spot in their rear view mirror waiting for them to leave. My dad does this, and I'm always just like "Aren't you taking more time away from yourself now too just to stick it to someone else?"