I'm pretty good at arguing, especially with stubborn idiots. Just always keep calm and talk with purpose and reason. Turn their idiocy against them, just like judo but with words.
Example Insult: HAHA HA!!!1! **** *** noob ****er!!!!, etc.
Example Response: Most of the civilized world does'nt seem to think so. Maybe you don't fit into that category.

If you do it well, they will probably just insult you again. Providing facts helps too, but never, ever yell back.

With reasonable arguments against reasonable people, just state your side of the argument and defend it with reason and fact.