Garfield hates Nermal because Nermal is a cute and playful kitten, which threatens Garfield's position as the cutest and most lovable pet in the household. Garfield is known for his jealousy and narcissistic personality, and he sees Nermal as competition for attention and affection from their owner, Jon Arbuckle. Garfield often tries to get rid of Nermal or show him up in various ways in order to maintain his status as top cat.
