The action of placing a towel on the floor (under the door) to cover the gap left between the bottom of the door and the floor. This will prevent any smells (like those created by the burning of illegal drugs) from escaping the room and contaminating common areas.
"Towel the door" can also be used as a command to someone telling them to do the action previously described.
If your gonna smoke, just stick a towel under your door and use a fan to blow the smoke out the window.
Kelly: Towel the door, bitch so this dank shit doesn't stink up the hallway.