If you eat something and no one sees you eat it, it has no calories. If you drink a diet soda with a candy bar, the calories in the candy bar are canceled out by the diet soda. When you eat with someone else, calories don't count if you don't eat more than they do. If you fatten up everyone else around you, then you look thinner. Things licked off knives and spoons have no calories if you are in the process of preparing something.
Examples are peanut butter on a knife making a sandwich and ice cream on a spoon making a sundae.
Foods that have the same color have the same number of calories. Chocolate is a universal color and may be substituted for any other food color. Foods that are frozen have no calories because calories are units of heat. Examples are ice cream, frozen pies, and Popsicles. Kate Purcell has submitted a bunch of diet humor which I'll list below.