You mentioned that you are fighting for your honor, and that this started when he called you and asshole. And you said to try and not talk you out of it... but, regardless of what insults were thrown, you shouldn't fight. You shouldn't have insulted him back, and you should have ignored his first insult. But it escalated, and got so bad to where you feel you need to fight to solve the problem.

Why not apologize first? Sure, your classmates might look down on that, but once you're done with grade school, nobody cares. It will not make you any less of a person to apologize for insulting this guy's weight. What others think of you for backing out of a fight and apologizing instead does not matter. I will say that I don't know the full situation; where you live, what it's like there, etc, but at the very least, don't put yourself into a position where you need to fight again. They are not a good solution to a problem like this.

I can't condone a fight for something like this, but if you're going to do it anyway... watch this video. It shows you how to punch without breaking your hand, and to actually do something. My masters liked to say spin + speed = power... and, that's true. This is how I learned to punch, and it works. Never leave your arm out there after you punch to give him an opportunity to grab you. Keep moving. Don't go for flashy; stick to the basics. Remember that your footwork is incredibly important. If you try to throw a punch and your feet are all over the place, it will be easy to get knocked to the ground.

Kazuhisa Hashimoto? He found it too difficult. 

You don't have to take the advice if you don't want. I do have a black belt in Taekwondo, so I am not completely ignorant of fighting techniques. I stand by what I said, and I would hope that you at least consider what I have to say, rather than disregarding it because my avatar is a pony.

EDIT: I quoted before your edit. Read the post. The first part is me telling you off because fighting is stupid. The last paragraph is my advice if you do fight.

EDIT 2: And actually, my opinions on fighting were set before I'd heard of the new MLP show. I got them from becoming a black belt. Above all, self control, avoiding fights, and only using what you learn for self defense is taught.

More than I can remember. I trained under master drunk street fighter Kimbo slice.

You may now pass to the next level.

How does it do that? Sure, the show is My Little Pony: Friendship is Magic. Sure it doesn't promote fighting. I also like the Resistance series and Left 4 Dead, where you murder all sorts of gruesome things.

Or, better yet, what if I play this game?