It's not really hating squirrels. Dogs are predators, and all of them have some amount of prey drive.
Dogs that chase are exhibiting a perfectly natural behavior. They are not being aggressive; they are simply satisfying their prey drive. Different dogs may respond to different triggers, though – joggers, bicyclists, cars, children running, fast-moving animals, including other dogs, cats, and one of their favorites, squirrels.
All canines are hardwired to chase prey. Without that vital impulse, dogs in the wild would never have had a chance at survival. Domestic dogs, of course, don’t need to hunt for food, but the instinct remains intact and manifests in some unlikely urges.
Tip! Some breeds are naturally more prey driven than others — Greyhounds and certain types of terriers are notorious chasers. But that doesn’t mean that impulse control can’t be learned and sharpened.
Teaching a dog not to chase takes time and effort — getting help from a reputable trainer is strongly recommended. There are, however, steps you can take on your own, read more at Dogtime.com.