Actually, in this situation, I would use the exact sentence that you have.
You could use "excitable," if you want to indicate that the dog might jump on a person.
You could use "disagreeable," if you want to let a person know that the dog might not appreciate being petted.
"Aggressive" could work.
For a person, you could use the word "moody." This won't be used with a dog most likely, though.