Final answer:
Mel's buying of a large pizza is an example of an impulse purchase, which is a spontaneous buying decision influenced by immediate emotions or product appeal.
Step-by-step explanation:
Mel's decision to buy a large pizza at a new fast food restaurant, despite his commitment to a healthy diet, is an example of an impulse purchase. Impulse purchases are unplanned decisions to buy a product or service, made just before a purchase. Such decisions are influenced by the emotions of the moment or the immediate appeal of the item, rather than by a careful consideration of the advantages and disadvantages of the purchase. This type of behavior is common, particularly within the context of fast food which is designed to be tempting and convenient.