When a gang boss wants you dead he may send someone to bring you to his office. The floor will have a plastic sheet over it so that when he shoots you and your body slumps to the floor, no one has to go through the trouble of removing the blood from the floor.
Standing on Plastic has evolved into a general term for someone powerful wanting you dead.
"Oh man, Chavez went crazy when I told him on the phone that I screwed up the vault job! He invited me to his office, I reckon I'm standing on plastic!"