When someone is so drunk, and desparate for a ride, that they will ride in the trunk of a car to get somewhere. Often times resulting in them passing out in the trunk- making for excellent black-mail photos!
I drove my two-seater to the party, but Cody needed a ride home. I told him he could ride in the trunk if he really wanted to. We got to his place and he was sleeping like a baby. What a trunk drunk!