Was bullied merciously in school, but I was always big (probably why they chose me) and would fight back. My opinion then is a bully doesn't want you to fight back. They may act like they do getting in your face, goading us, etc. but as with everyone else, a good punch in the nose forces a reassesment and "if this really worth it?"
When you think of bullies kike a predator on those wildlife shows, they're looking for the easy meal. The weak, lame, on sick. Not the able-bodied who pose a threat to them. So if you act like prey, you'll become prey. Act able-bodied and they'll pick someone else.
What I've learned from behavioral science study is if you make eye-contact you can avoid looking like prey. As you go about your business, if known bullies come around make eye contact with them. Let them know you see them and aren't worried about it. If they move on you, wait for them to get within strike distance then let them have it, right in the face. It's NOT what they want and few expect "prey" to haul off and smack em upside the head.