This can be very annoying if you are merely dropping off cumbersome bags in order to resume retail therapy/madness without having to carry the stuff around. By the time you get to your car, you realise creepily that someone has been watching you for at least 10 minutes, maybe longer if the stalker has telescopic equipment, and they are already there, watching with squinty eyes and the signal light blinking to warn others that the car parking space belongs to them and to let you know in a non-verbal way, that you had better get the hell out quickly!
This is particularly annoying if you are starving, have picked up something to eat, and just want a few minutes peace and quiet to nosh in the privacy of your own little space. You feel obligated but annoyed to see someone waiting. You either pretend not to see them, or signal that you have food, signal that you aren't actually leaving if that's the case, or if you're really a pushover, just leave even if you didn't want to.
Also known as a Parking Lot Stalker.
Most people have sat on both sides of the fence in this situation so most of the time both parties handle it in a civilised way.