The Gag Test
Anything that make you gag is spoiled, except for leftovers from what you cooked for yourself last night.
When something starts pecking its way out of the shell, the egg is probably past its prime.
Milk is spoiled when it starts to look like yogurt. Yogurt is spoiled when it starts to look like cottage cheese. Cottage cheese is spoiled when it starts to look like regular cheese. Regular cheese is nothing but spoiled milk anyway and can’t get any more spoiled that it is already . . . unless it’s getting blue and furry, then you’d better back off.
If it makes you violently ill after you eat it, the mayonnaise is spoiled.
Frozen foods that have become an integral part of the defrosting problem in your freezer compartment will probably be spoiled by the time you pry them out with a kitchen knife.
If opening the refrigerator door causes stray animals from a three-block radius to congregate outside your house, the meat is spoiled.
Fresh potatoes do not have roots, branches, or dense, leafy undergrowth.
Putting empty containers back into the refrigerator is an old trick, but it only works if you have a wife or a maid.
General Rule of Thumb
Most food cannot be kept longer than the average life span of a hamster. Keep a hamster in your refrigerator to gauge this.