The coffee ritual.

Every morning, Caren buys a cup of coffee on her way to work.

The coffee cup sits on her desk all day. To my knowledge, she has never drank more than half a cup, even though she buys a large.

At the end of the day, Caren microwaves her coffee cup, which is made of styrofoam, and takes it with her in the car for the ride home.

She never drinks the coffee in the car, and yesterday's coffee becomes today's ashtray.