Disclaimer: Naruto is not mine.
Sasuke hated the dog until the day it died.
Naruto slathered it with affection. He bought it ridiculously expensive treats and paid for it to be professionally bathed every month, even though it would immediately locate the nearest mudhole to roll in before slobbering all over Sasuke's clean clothes.
The dog's greatest offense, however, was how friendly it was. Naruto would spend hours playing with it until he was so exhausted that he fell asleep the moment he hit the mattress.
When the dog died, Naruto was heartbroken. Sasuke would have felt guilty, except he loved comfort sex too much.