While it can be argued that standards of behavior may be different in the virtual world, they certainly should not be lower. You should do your best to act within the laws and ethical manners of society whenever you inhabit "cyberspace." A good rule to follow is that if you wouldn't say it to someone's face, then you shouldn’t say it online. Name calling, cursing, expressing deliberately offensive opinions – if you wouldn't do it to the face of anyone who might conceivably see what you write, don't write it. All caps are generally perceived as yelling, while all lower case implies a lack of education and/or self-confidence. Text "slang" is nonot appropriate. And, please don't forget to say please and thank you as appropriate.
Avoid using offensive language or making personal attacks in online discussion, just as you would not do so in face-to-face conversation.