I should point out, that as a portrait photographer for hire, we have certain locations, depending on time of day, lighting, subject matter in our minds when we venture out to do outdoor shoots.
When we arrive at them and someone is there, our first reactions is always, "oh shit". We can come by here a thousand times a day and never a soul around, and then when we go to shoot there, someone is parked there.
I used to have a favorite family, wedding site with great light, trees etc and soon some wannabe photographers started using "my" spot so I couldn't use it any more. (only so much time after a wedding)
What really pissed me off was they were shooting with a fucking flash on their cameras so their pictures were crap anyway. (I saw some of them, flash blasting out the available light) And I used it for a natural background and a natural direction of light.
So as photographers we can get pretty pissy and possessive about our "spots".
I just usually politely say something like " Get the fuck out of my spot asshole" and that seems to work.