Why would my dog hate my best friend?

You’ll probably never know – they just sometimes have odd preferences. My border collie (who, granted, is a freak) expresses his anal glands every time my 95lb friend Barbara comes over.

There could be a smell on your renter your dog doesn’t like or associates with something threatening. Also, as dumb as it is to us humans, some dogs see darker complected people as suspicious- something about the shades of gray they see.

I don’t think your dog hates your best friend that is an emotion that we, humans, label certain behaviour of animals, but he/she is just barking at her, probably because there is something that triggers her/him to feel threatened or that makes him/her scared, etc.
Could be the use of perfume, the loudness or tone of her voice or one of the things that @Neizvestnaya stated or the way she pets the dog, etc.

Your dog could be jealous of your best friend. Have your best friend offer the dog treats. First, she should just put the treat down and back away. Then she should gradually get the dog to come closer before giving her the treat.

If the dog is small, have your best friend sit down quietly and work with the dog.

Is your “best friend” made of cats?
Or have some kind of ‘catesque’ connection?

My cat hates my best friend because the two of us together can be kind of loud and obnoxious and my cat likes peace and quiet. Seems stranger for a dog though. Does your dog seem to dislike noise or anything like that?

Like the above smell answer. It might take contact with another pet and that smell make him act “Crazy”.

One never knows with animals, but, they do possess senses far more in tune than ours.
Either it’s a weird scent thing, or…your friend is evil. Haha
My dear departed old Siamese “Jerome” pooped on my ex husbands pillow and peed on him in bed…that cat was trying his damndest to warn me! Poor thing! LOL

Maybe your dog is just a bitch. ~

Does your best friend hates dog, in a way? Dogs do somehow feel it naturally, you know.