We'll start with an epiphanette vouchsafed to me by an insightful friend:
Offence can never be given, only taken.
In other words, before you can offend me, I have to allow you to do so.
It's understandable that many people don't realise this - given a strong emotional reaction to a subject, I may instantly feel offended by something someone said. I make no conscious decision, and the only action I perceive is the original statement - it looks like simple cause and effect.
However, the important word is perceive - sure, it looks to me as if my offence was a direct effect of the statement, but that's not actually true.
Offend me. No, really - go on...
Call my mother names. Impugn my political affiliation. Assert things about my sexuality. Go on - post comments or e-mail me, if you like. All of these things can be reliably guaranteed to cause offence to people, but I promise I won't get offended by any of them. How can this be?
It's because I've simply chosen not to take offence at them. This much is obvious, but wait - if a statement is or is not "offensive", how can I choose whether or not to be offended? If "being offended" is a direct consequence of the statement, how can I opt out, and merely decide not to be?
The point here is that being offended is a choice. It might be the default choice - one I usually take automatically, or without even being consciously aware of it - but if I can choose not to be offended, surely that proves the opposite choice (being offended) is also a choice?
If offence can only ever be taken, then the "offensiveness" is your reaction to a statement, not a property of the statement itself. Moreover, it's not even a reaction the speaker can necessarily predict ahead of time - I make a statement, and then you decide whether you're offended by it.
Always remember this fact - every time you are offended, it's because you have chosen to feel that way. The nasty feeling you have is a direct consequence of your choice, not of the statement which motivated it.
The case of deliberate provocation
Obviously, some statements are made with the deliberate intent to offend you. It's understandable (though not admirable) that in these situations it's hard to overrule that emotional reaction - when someone tries to insult you, it's hard not to be offended.
To see why this is a problem, let's reason by analogy:
When babies are born, they have no bowel control - if their bowel is full, they'll shit. As far as the baby's concerned it's an automatic process.
However, as we grow and develop we learn that although excreting is an automatic process, we can learn to make it a conscious choice. Even if (through some biological problem) we can't do this, we at least recognise it's a fault within ourselves and strive to ameliorate it (for example, with diapers, medication, colostomy bags, and the like).
What seems like an automatic process we have no control over can - with recognition and effort - be mastered and controlled. And the more we practice it, the less difficult it becomes, until our chosen option becomes the automatic one (seriously - when was the last time you took a conscious choice not to shit yourself?).
Likewise, although "being offended" feels for many people as if it's something beyond their control, this is an illusion caused by their own lack of self-control. It's effectively emotional incontinence.
Given this, how fair is it to demand others change their actions based on a flaw within ourselves? It seems to me rather like demanding that everyone else carry around a potty at all times, just in case I want to take a shit.
Applying this reasoning to incontinence makes the reaction seem ludicrous - obviously my lack of self-control is my problem to deal with. Anyone who insisted everyone else has to scramble to solve their own problem while they themselves did nothing would be considered enormously selfish, demanding and immature.
So why when the issue is an emotional lack of control do so many people insist others change their behaviour, instead of asking what it says about them?
Can we as a society stop thinking of "offendedness" as a blameless condition, and start thinking of it as a lack of self-control? Can we stop advocating banning "offensive" things, and instead strive to fix the flaws within ourselves that mean they bother us so much?
Please - if you've remotely enjoyed this post at all, I want you to promise me something. Next time you read or hear something really offensive - something that really makes your blood boil - do me a favour.
Instead of shouting back or demanding something be banned, I want you to sit back, count to ten, and ask yourself
Am I shitting myself in public?
And if you are, and you decide to do it anyway, and then blame it on someone else, what does that say about you?
 Epiphanette: like an epiphany, but less-so. An interesting little thought that explains something fairly profound, but isn't really world-shaking enough to qualify as a full-blown epiphany. And no, sadly, it isn't a real word. ;-)