Well, you've got your self in a pickle, haven't you?

"I then insulted him back very badly..." I'll be blunt: this was a big mistake. Do you know the nursery rhyme beginning "sticks and stones..."? In my opinion the smartest thing would have been to walk away. If you doubt me, consider what your efforts have brought you so far: fear and potential danger.

Now do you really want to escalate the "war" by arming yourself?

First, you should be aware that being in possession of a weapon without a lawful excuse is illegal in almost every first world country. "Self-defence" is usually not an excuse, unless you've picked up a stick from the roadside just before/during an attack. Check the law in your jurisdiction before you decide to pack the brass knuckles in your backpack/pocket.

In my State in Australia you would be facing a serious fine or possibly imprisonment for the possession alone.

Second - do you really think it would be smart to hit him with brass knuckles? If you hit the guy with this weapon and seriously injured him you'd have a tough time convincing a jury that it was "self-defence". They'd wonder why you went out "armed" in the first place (it will be hard to shift the impression that you were looking for him so as to beat him up). I'm afraid you'd come across as a common thug - particularly with your weapon of choice, a brass knuckle. I'm not being judgmental about this bit, just a realist - I speak as a former court lawyer.

You'd almost certainly do time if you injured him. If you killed him you go for manslaughter or even murder. You'd go away for a very long time.

Please take the time to consider your next move very carefully...

What you want to do is diffuse the situation - not escalate it to a full-on war. I won't suggest how you go about this - only you will know, given the vagaries of your situation.

Good luck. Btw - "cowardice" is the last thing you should be concerned about.