Food Spoilage table.

EGGS
When something starts pecking its way out of the shell, the egg is probably past its prime.
DAIRY PRODUCTS
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 than it is already.
MAYONNAISE
If it makes you violently ill after you eat it, the mayonnaise is spoiled.
MEAT
If opening the refrigerator door causes stray animals from a three-block radius to congregate outside your house, the meat is spoiled.
LETTUCE
Bibb lettuce is spoiled when you can't get it off the bottom of the vegetable crisper without Comet.
CARROTS
A carrot that you can tie a clove hitch knot with it is not fresh.
CHIP DIP:
If you can take it out of its container and bounce it on the floor, it has gone bad.
GENERAL RULE OF THUMB - if you can't find it on this list:
Most food cannot be kept longer than the average life span of a hamster. Keep a hamster in your refrigerator to gauge this.

Courtesy of The homemakers mentor