I like this board, and because I like it I'll try and help you out by giving it to you like it is. I, hopefully unlike you, had to learn the hard way, but that doesn't mean I should have or needed to.
First off, get real. Ever heard the term, "keep it real?" Well, ask yourself what the fuck you are doing asking self-defense advice from a bunch of internet logins in the first place, aside from showing how very green your cherry is. You don't know what to do, so you throw it out there and hope you get lucky.
Well, you did. I'm going to tell it to you like it is.
This isn't a duel between gentlemen. If it was, he wouldn't be running his mouth off and you wouldn't have asked for help. The two of you would have already settled it between you, face to face, showing the respect that someone desserving of it himself values.
With your attitude, you need to wise the fuck up or stick to dialing 911 when someone fucks with you. This isn't a ring with a ref, your corners, and security. If the problem was about who fights better, you could move it there.
This guy is running his mouth because he needs to get fucked up real good by someone for it and because he's pretty sure you are just going to bend over long enough for him to get his rocks off. Until he learns (everybody does eventually), he's enjoying all the phony respect he gets doing it. This is the perfect opportunity for you to learn the EASY way what he needs to learn the hard way.
Since its a private issue, YOU need to go and find HIM; preferably when he's alone or outnumbered. Why let him hunt for you? How fucking stupid is this? Think about it. What if he finds you at work, with a girl, or with friends or family?
Find out where he lives or where his girl does, or anywhere he's likely to be alone, post up with two or more big dudes or good friends, and have one of them stand outside the car (the less ghetto of your pals) to watch and talk to people. You can also have one of your girls bring him to you by playing the role. Chicks are so good at this.
When he shows up, have your friend smile and talk with him long enough to draw him close. Have your other friend(s) get out and join the conversation; boxing might be a good topic to discuss, or have your friend address him by name and act like a friend. Don't wait too long before you get out yourself. Don't be shy. You've got him by the balls, now.
Walk right up to his face, look him in the eye, and ask him why he's been running his mouth. Have one or two of your friends walk around the sides and stand behind him as you do this; arm's length. Unless he's got serious heart or is protecting someone else, he'll back down apologizing for the misunderstanding without pushing you back or swinging. If he does attack (he won't) your friends can grab him from behind before he can fuck you up too badly, and you can now choose whether to duct tape his ass to a chair (ankles and knees around two front legs of chair, stomach and chest around back of chair, and wrists behind back with tape running up around neck, mouth, ears, and forhead - head tilted back) or whatever the fuck you want; you could make a citizen's arrest and call the po-pos - you'll have witnesses to his attack and can take photos of his ass tied to the chair for later use.
The possibilities are endless, but try not to break any laws while you deal with him. Hopefully, what shouldn't take more than an hour to accomplish will end it before anyone gets hurt.
Until you can set it up, which shouldn't take more than one day from now, walk with a cane, a chain with a lock on it, or a bag with a glove, ball, a bottle of water, and a wooden bat with handle out the zipper in it too and from your car; a six foot chain with a master lock on the end can brain a fucking cow, so go easy.
90% of the time they just back down or tell it to you like it is without trying anything, the later being what anyone worth a shit would do not pissed or stupid enough to volunteer for a good fucking over. Remember, he's been running HIS mouth about YOU, and if you want to be able to walk and talk like you have a pair or at the very least learn how it feels to do so, you're going to have to earn it.