Autism

Most of the bullies I dealt with were in college or business jabronis in the workforce since I was homeschooled (that's a rant for another day) so YMMV. I also stopped getting bullied physically by everyone except my parents as a small child, so I don't have any advice for that.

tl;dr: bullies stop when it's not worth picking on you.

There's no one-size-fits-all solution, but these have all worked for me with various people bullying me verbally / emotionally.

Hippie shit:

Understand why they're doing this: most of them are deeply insecure about something and are deflecting from that. You could figure out what that is and make fun of it, but that is the path to the dark side. Instead, acknowledge it in your head. "He's picking on me because he has a stutter." "She got frozen out of her friend clique because they think she's weird and is lashing out." It's amazing how that knowledge helps you ignore whatever they're saying. State of mind is key. They morph from some awful monster you have to hide from into a pathetic jerk that has to put down other people to feel ok.

Just straight-up gray rock them. They need a reaction. One-syllable responses ("huh", "yep", "really?", "ok") are not fun for them and most of them will move on to easier targets.

Do an image audit and makeover: get some nicer clothes, change your hair, take care of yourself. This boosts self-esteem and also confuses the bully. They'll probably have new material once they unblock their second nostril and get enough brain oxygen to do serious thought, but you can be ready for that. My little cousin was getting bullied in middle school, and my aunt's solution was to buy him brand new clothes, give him a faux hawk, and get his ear pierced. It worked!

This one's innate for me, but I have what my wife refers to as "resting warlock face." I assume it's mostly just a look of grim concentration trying to navigate the universe, but it mostly just looks like I'm trying to set whatever I'm looking at on fire with my mind. People generally do not want to approach that.

Chaos agent shit: The following can be used to great effect, but might also get you punched. Deploy with care. Getting punched is not a good way to deal with being bullied.

Aggressively refuse to understand what they're saying. Ask a lot of questions. When you finally decide you've figured it out, say "OH, you were making fun of me! You should lead with that next time." Next time, interrupt with "just to clarify, you're making fun of me right now? OK. It's hard to tell with you." and then fold your hands and stare directly at their forehead / nose / whatever works, expectantly. This takes some of the power back, throws them off their script, and makes the whole encounter deeply unfun.

Be funnier. I discovered George Carlin during his post-shilling for AT&T phase, when he was good and angry. It's amazing how he puts sentences together to convey maximum vitriol in a funny way. I listened to him obsessively (also Eddie Izzard, Mitch Hedberg, Dylan Moran, and lots of others) and can fall into a rant mode and get the crowd back on my side. Bullies want easy, predictable targets. Being funnier than them changes the power dynamic and makes them want to disengage.

Keep the riff going without them. "You fucked my mom? Did she at least charge this time? I keep telling her that she can't keep taking charity cases. If you're good at something, never do it for free." I found I could always go grosser and darker than the bullies. If they get uncomfortable or cross a serious line (or you're uncomfortable going further), end with "we were having a nice conversation about [whatever the original subject was] and you had to make it weird." Don't go so far you become the bad guy; I keep racial/gendered/ableist stuff out of my vocab.

Good luck and to reiterate, don't do chaos agent shit if it'll get you punched.