Have been thinking about this thread quite hard - there are some interesting issues here.
I actually think Nightynight may be right that the man quoted may not have been referring only to women - looking at different definitions of slag on internet dictionaries (!) it does seem to sometimes be used of both men and women. I'm sure I've heard men on Britflick gangster movies use it of men, too.
However I stand by what I said before about 'slag' expressing not just disapproval, but real hatred, and I think this, for me, is why the whole thing is so chilling, whether it refers to just men or men and women.
From what Nightynight says about the one time she has used the word, it was clear it was under great provocation - and quite frankly if someone throws something at you and you use whatever word is the most hurtful that you can think of to throw back to them, good luck to you. But the fact remains that it is a word that for most people has strong sexual connotations and if someone is prepared to use the word in cold blood they are basically signing up to a code that says that people who sleep around are worthy to be hated because they sleep around. If someone threw something at someone or set their toddlers fighting and we knew they were of unimpeachable moral rectitude sexually, I'm guessing 'slag' wouldn't be the word that would come to mind.
Now personally, I have done some good things and some bad things in my life and would be open to criticism for plenty of reasons. I have also (when I was a student and long before I met my wonderful dh, to whom I am totally committed) slept around and had some one-night stands. I am not proud of this because there is no reason why I should be, but I am also not ashamed of it.
If someone calls people at a nightclub slags because of their sexual behaviour, they are also calling me a slag.
I am quite prepared for someone (whether Muslim, white male misogynist or old lady) to disapprove of my sexual behaviour, even to 'judge' it, but the idea that it makes me some kind of rubbish or worthy of hatred, well, that freaks me out.