In any case it is worth remembering that in the Internet are to some extent become equal. When the dispute comes to global problems of philosophical topics, your interlocutor will be completely do not care what you have it twice as old and has not one entity. The network has an image. It is created from the messages of human thought. It does not get to hide behind the status of appearance, because of personal dependence.
This property has a downside - practically nothing, spoken of in the online skirmish does not apply to you personally. Subjected to harassment you create a character or some your belief. Even if the offense intended to you personally, do not take them at their own expense. After all, you and your opponent hardly know - except here we can have constructive criticism?
Your friend will also tries on different roles. It can be normal "Internet troll" answer which simply makes no sense. You see that all messages seem quite delusional and catch between them some connection fails? In response to your claim further whet the enemy, and tons of obscure slang and spilling into your address? Just ignore this conversation. Not having mastered all the intricacies of Internet communication, slang and manners, you still can not prove their point. Besides, this is usually not required, because the "troll" is absolutely not interested.
Another thing, when the insult causes adult. Here you can develop the discussion in the usual style for you. Meet the same or not - depends on your beliefs. Constructive dialogue can develop into a conversation, "who gets smarter." If this type of discussion you're not ready, better to end the conflict. You can simply write that you are not interested in such discussions, and you leave the other party the right to keep their opinions to themselves.
It's true - to convince every person on the Internet will not work. Therefore, take the time to impress someone their beliefs and ideas - just pointless.