Let's go over this again, shall we?
The Fundamental Rule of Parking Lots clearly states that once a car has pulled into a parking space, that car owns said space until the driver pulls out of it. For example, when someone returns to their vehicle after, say, spending thirty minutes in Target, they do not have to move their car until they damn well want to.
The rule also states that any driver that pulls next to a parked car, intent on taking the parking space when it opens, and expresses impatience at the pace at which the car already parked is leaving, shall be referred to as an Asshat. Additionally, if multiple open parking spaces exist within fifty feet, he/she/they shall be elevated to the title of Festering Asshat.
(Side note: although not encouraged, if the driver of the parked car is in the process of putting their fourteen month old son into his car seat when the Asshat makes its presence known, it is acceptable to fling a dozen rotten tomatoes against their windshield.)
So let's review: a car in a parking spot is entitled to that spot until it leaves. The driver is not required to acknowledge anyone interested in said spot, nor give a rat's ass about them. If the driver of the parked car wants to have a pizza delivered and eat it in the car, they may do so.
Any driver skulking in a parking lot looking for a space should assume that any and all parked cars are empty, and will be remaining there for an undetermined amount of time. Move along.
Don't be an Asshat. At least not while I am around.