Hmm. It’s an interesting one, this. Haven’t read the whole thread yet so apologies if what I’m about to say has already been said (and probably more succinctly!)
I don’t condone calling any one a slag based on either their dress sense, general appearance, attitude, number of sexual partners etc. It’s a horrible word used to belittle women and keep us in our place.
However… do I make judgements about people based on how they present themselves? Absolutely. And I think most of us would be lying if we claimed we didn’t.
If you’ll allow me to blow my own trumpet for a moment, I’m not a bad looking lass. Decent body, fit and conventionally attractive (or so my experiences lead me to believe.)
I don’t feel the need to flaunt it or draw attention to it when I’m not working.
I work in the sex industry and spend most of the day trussed up in stockings, high heels, plunging necklines and tiny skirts. I’ll be damned if I’m wearing that shit for fun in my free time. It’s not comfortable or practical, and it’s all designed to show off the female form for male attention – that’s the bottom line.
Why would anyone subject themselves to the discomfort of this stuff unless they were doing it for the attention and fleeting, flimsy validation that comes from people admiring/envying your body?
‘Oh but I wear it for myself not for men or other women!’
Aye… ok. If someone can tell me how dressing like you’re in my line of work benefits you in any way, I’ll happily listen and reassess my judgement. 
People are entitled to wear what they want (within reason) but, to me, a tiny micro-skirt and see through blouse when you work in an office entering data into spreadsheets just screams low self-esteem.
I don’t think these women are slags, I think they lack confidence in their other attributes so rely on their bodies/looks to carry them.
It doesn’t stir envy in me – it makes me angry that we live in a world where a lot of women feel they are more valuable when they have less clothes on.