I would jut love to say something to those I see walk right out the door. There was someone in our office like that a few years ago. No one would go near her at anytime. No one would have break or lunch with her, no one would enter her cubicle. nada. Finally, someone did say something to her - quietly and privately. She left shortly after.
The only reason I haven't said anything to those I've seen walk out - you don't know how they are going to react and I really don't want to have to pick myself up off the floor.
I don't believe an adult doesn't know exactly what they are doing when they walk out of the bathroom without washing their hands. They are ignorant, plain and simple.