I've let my children eat food that has fallen on the floor.
I suppose I should write that in the present tense, as it occurs with frequency. I let my kids eat food that falls on the floor. If my child was to drop a piece of food on your floor and you were to say, "Hey, three second rule!", my child would look at you with a blank expression. Haven't introduced that phrase. It's more of a pick it up and eat it now, later, whatever.
Of course there is the exception - we don't eat food that has fallen on public bathroom floors, I'm sure of it. However, I cannot even picture a time when I was in a public bathroom with my children and they were eating. Huh. I guess I don't have to worry about that much. Oh, and under the table of a restaurant if the floor is really gross. It's hit or miss, but I guess I strive to teach my children to leave it be.
C'mom folks. What's your food on the floor rule?