When idiots meet.
I've definitely encountered this and believe me, they did not get the space. I will explain to them that they can stand there all day but they will not be parking there unless they can go through my car somehow.
If this was on a city street in L.A. and a cop comes along, they would get a talking to and be arrested if they didn't fk off. It's illegal to "guard" a parking spot.
I'm putting a semi air horn on my PU truck specifically for situations like this.