My window at work looks out onto the back parking lot, so every time I stand up to stretch in a feeble attempt to keep my wrists and back alive for just a few more years, I see all the horrible parking jobs perpetrated by my fellow employees.
The most frequent breach of parking lot etiquette is the one illustrated in this photo. The owner of the silver Honda on the left has erroneously parked in an area that is not a parking space. In actuality, this area is, for lack of a better term, a "backing-out area" provided for the convenience of the cars occupying the two spots directly bordering it. If there were another car next to the Honda and a car in the leftmost handicapped parking space, the silver BMW would have a very hard time backing out of his space and the handicapped fellow would find it nearly impossible.
In this particular parking lot the backing-out area isn't clearly marked as such, but anyone with two eyes and a lump of clay between their ears should be able to figure it out based on the lack of white lines and its proximity and position in relation to the bordering spaces. And yet, every day there's at least one car parked there; often two.
I wish I knew whose cars they were so I could shun them in the halls and give them dirty looks in the break room.