I don't tend to get asked because I don't show my scars very often but I am never offended when I am. I've met two people who have bitched about my scars etc in my time and one of them, my friends saw to and it hasn't happened again. The other one, in my eyes, just doesn't exist. To be honest though, my mum made me lie about them or covers up for me if people ask and she's there. I think that my family are more embarrassed than I am because, although I am 'only' 19, I would be inclined to say that it is something I used to do and hope for the best from that.
As
Tokoloshe said, it's more about raising awareness and the scars I have on show are not the recent ones and are more faint, so I don't think it matters as much as people think it's not so much of a problem and are less freaked out by it.
In front of a load of people though, explaining your way out of that one is embarrassing.
+ coming on from what
Downside said, people in Africa do tend to ask but, as they do not understand self-harm in the slightest and are such inspirational people, it's easy to tell them that you had an accident when younger or to lie. The people there are more likely to believe you anyway and the reason they bug you is because they hold the English (or white people) in such high esteem that they want to look after you and make sure you're okay in every way, shape or form.