Eggs: When something starts pecking its way out of the shell, the egg
is probably past its prime.
Meat: If opening the refrigerator door causes stray animals from a 3
block radius to congregate outside your house, the meat is spoiled.
Flour: If it wiggles...it's spoiled.
Lettuce: Bibb lettuce is spoiled when you can't get it off the bottom
of the vegetable crisper without Comet. Romaine lettuce is spoiled when
it turns liquid.
Raisins: Raisins should not be harder than your teeth.
Potatoes: Fresh potatoes do not have roots, branches or dense, leafy
Chip dip: If you can take it out of its container and bounce it on the
floor, it has gone bad.
Unmarked item: You know its well beyond its prime when you're tempted
to discard the Tupperware along with the food. Generally speaking,
Tupperware containers should not burp when you open them.
Frozen food: Frozen foods that have become an integral part of the
defrosting problem in your freezer compartment will probably be
spoiled (or wrecked, anyway) by the time you pry them out with a
hammer and knife.