Lampshaded: "Hey, Bob, do you mind if I get rid of this, or are you doing a science project on the regenerative properties of three-month-old tuna casserole?"
Invoked: Bob is very forgetful, and puts a Tupperware container in the fridge.
Defied: Bob reminds himself to clean the fridge at least every couple of months and not allow food to stay in the fridge more than a week or two. He also keeps the fridge and freezer at a low enough temperature to keep micro-beasties at bay.
Discussed: "It's a wonder Bob hasn't died of food poisoning!"
Deconstructed: Obviously, it presents a real health hazard.