I worked as a waiter for three years, and while I never spat in anybody's food, I saw it happened and admit that I was tempted. I did other, more harmless things to bad customers though (like letting a $35 rack of lamb sit under the heat lamp for about ten minutes...oops). You reap what you sow...my good customers got free drinks and desserts.
"You travel alone because other people are only there to remind you how much that hook hurts that we all bit down on. Wait for that one day we can bite free and get back out there in space where we belong, sail back over water, over skies, into space, the hook finally out of our mouths and we wander back out there in space spawning to other planets never to return hurrah to earth and we'll look back and can't even see these lives here anymore. Only the taste of blood to remind us we ever existed. The earth is small. We're gone. We're dead. We're safe."
-John Guare, Landscape of the Body