Coping mechanisms?

He's trying to bully and belittle you and undermine your confidence just because he thinks he can. And you need to prove to him that he can't. And that applies even if he is in some way mentally challenged.

Do as others have suggested and keep you phone handy and if you see him approaching hit record and make sure he knows it's pointing right at him. Tell him once very clearly exactly why you're doing it and that you'll keep on doing it every time you see him until such time as he stops or you decide you need to take that decision out of his hands by reporting his behaviour.

He's 60 and you're a teenager and it's not right for a man of his age to exhibit such worrisome behaviour towards a kid he doesn't even know. And no, it's not fair that a kid should have to play the role of the adult but if you don't things will never get better. Good luck. 👍️

Put a huge sign in your yard, WITH A FINGER pointing to your neighbors house:

HELP!! THIS OLD MAN HAS BEEN VERBALLY HARRASSING ME FOR FOUR YEARS!

I'd tell him to fuck off

Start taking diapers out with you.
Point at him and laugh you ass off at him and and toss a diaper at him and talk to him like your talking to an infant.

Speak up, tell someone. If you feel unsafe, call the authorities. That’s what I would personally do

Confront the grumpy old bastard, and tell him to shut the fuck up. The more you ignore him the stronger the abuse will become

Call the authorities and sue him for harassment. Sounds like a small claims court issue. Make enough legal trouble for them that they stop or have to move. Also get a support network going of people you can depend on.

It is harassment. You need to record him doing it. If his attacks are profane...that's against the law as well. Record it a few times then call the police and show them the video. In this day and age you could probably sue him for emotional duress.

It depends on the law where you live. In some places you can get a protection order against him.

If at all possible, record his abuse on a video on your cell phone. Make detailed notes about what he said to you on what day and date.

If he did that to me - I would just stand there recording him not saying a word --he he he

Point out the differences in your age and fitness levels and tell him you'd drop him like a bag of sand so stfu.

Offer him a smile and a hearty nod of recognition.

I just realized what you actually asked. First, is it 'only' uncomfortable, or does he scare you?