When your dog depends on you for every little thing because it has attachment disorder. Also when your dog is your best friend because you spend so much time walking it, cleaning up its shit etc.
Also when you meet a new besty because they approach you at the dog park to compliment you on how cute your doggie is.
Basically pertaining to everything involved with friendship, dogs, and such.
I made a new doggy besty when I went to the park yesterday.
My roommate's doggy besty is a pit; she attacked my kittie but my kittie scratched and bit back.