I don't want to walk my roommate's dog.
Do you have a problem with the dog?
No, I just don't feel like doing it.
I know you don't want to do it, but you really should take your roommate's dog for a walk. People are supposed to help each other out with small requests. If you refuse then your roommate might not help you out in the future.
Fuck you. I don't need someone else telling me what to do!
If you're not going to help out your roommate with this small chore, they might not want to be roommates with you anymore. They will potentially try to find somewhere else to live.