While I did a brief outline of media law, something this post from David raises is harassment. The law in most democracies that have harassment (religious, sexual and so on) legislation follows the same model, and it is the opposite of the Facebook slanging match that David describes. The law is quite clear that intent is irrelevant – if someone experiences your comments or behaviour as offensive, or harassing, then they are. In other words, if I use some slang term to describe an ethnic group and someone finds it offensive, I cannot claim that I didn’t mean anything by it, that some of my best friends are ‘x’ and they don’t seem to mind the phrase, and so on. It is offensive as someone has found it so. Here, the rights are firmly on the side of the recipient, and you can see why, since intent (“but I didn’t mean anything by it”) is a licence to not have to acknowledge the rights of others. Remember, this includes harassment. So if I touch your shoulder as your teacher and you find that uncomfortable, whether I intended anything by it or not is irrelevant. The law takes this view as harassment and so on usually involves a power inequity, and so it is those in the inequitable position that need defending.
This means if you post something, and someone finds it offensive, it is. The test is whether a reasonable person would regard it as offensive, and this is a very broad test.