There's really no easy technique to just knock someone out like that without actual training.
Even a good left/right hook to the jaw isn't going to work if you aren't strong or fast enough. Certainly grappling moves would be impossible and dangerous to explain over the net.
Furthermore, even if you do knock him out what happens when he comes to get revenge? What if he's a competent knife fighter or if he's got friends who don't mind disfiguring you for life or worse? There's really no way you can tell. Best idea is to stay clear of him and stick around as many people as you can all the time.
If he provokes you, walk away. If he tries to hurt you, run to a crowd of people you know. There's no shame in running. If he picks a fight, he knows the ground he's on and already has the advantage. If nothing else, running will take away that advantage.
My advice if you insist on learning something would be to go learn boxing, that's about the fastest fighting technique to learn. Only 5-6 techniques to remember. Build your power on a heavy bag and train (shadow boxing) every day. NEVER LET DOWN YOUR GUARD. Do light weights with high repetitions to build power in your shoulders and arms.
We are not trying to "sound wise and noble", we're trying not to help you do something stupid which will get you hurt. The best way to avoid getting hurt is to avoid situations where you have to fight. Simple. If we tell you a technique that seriously injures him then we might be liable for telling you. (Not sure about that one, but depending on the country it might be true)
If you are concerned for your safety in future take up an MA to balance out the boxing techniques. (Preferrably either Muay Thai or a grappling MA, such as Jujutsu)
Hopefully you'll never have to use the boxing or MA skills you learn in a real fight.
NOTE: BEFORE YOU DO ANYTHING ELSE I RECCOMMEND READING THIS SITE. www.nononsenseselfdefense.com
[This message has been edited by Leo_E_49 (edited 03-05-2005).]