When the back seat of a car is filled. Both window seats and bitch is taken, sometimes double bitch is taken into effect. So there is absolutely no space, not even for one more cheek. The last person has to get a running start and dive across all the people sitting in the back seat and lay on top of their laps.
Brian (last person to get in, window seat) "Danny, looks like your trunkin it"
Danny (standing outside car) "Nah fuck that, let me get diver"