I don't feel like helping my friend look for his dog.
As a friend, why would you not help look for your friend's dog?
He was mean to me on my birthday.
Even if he was mean to you, you need to help your friend out. Your friend is worried about his dog and you should help look for it.
I'm really pissed that he was mean to me on my birthday, maybe he should have took me out. I'll get back at him by not trying to find his dog.
You are usually very forgiving, so I am surprised you are holding onto this grudge. I would think if you find his dog, he will be super grateful to you and probably feel guilty about being mean to you on your birthday. Wouldn't that be the best revenge?