Talk to me about the word 'slag'.

Of course it's sexist. Your acquaintance is a massive misogynistic bell-end.

This.

What is the male equivalent ?

Stud!!!

Of course its sexist and your explanation to step daughter is spot on

It usually means a woman who sleeps with someone else and won't sleep with me

As opposed to frigid which means a woman who won't sleep with me and as far as I know isn't sleeping with someone else

Mostly said by men.

If said by women, it means woman who slept with someone I fancy who doesn't fancy me.

You know I used to hear this word all the time always used to shame women. Don't really hear it now.

Legend apparently

Do you really have to ask? Sorry but this is a bit like "Water- is it wet? Discuss"

The only context I can think of where it might be used for a man is amongst gay men about themselves. I've heard, very occasionally, gay men use the word "tart" about another man but it doesn't have anything like the viciousness of similar insults applied to a woman. I'm guessing however your acquaintance probably isn't a camp, gay man.

What are the origins?

As opposed to frigid which means a woman who won't sleep with me and as far as I know isn't sleeping with someone else

At 18 my boyfriend was told by a boy I’d slow danced with once that I was frigid

How can you tell from a slow dance!

Nasty names from nasty people

Auntie google suggests oriogionally used as slag, detritus from mining etc, started to be used in 1700's as a person of no worth, by 1900's to mean slut

Your acquaintance might cite this as proof it's used for men.

youtu.be/AVSWAAOaBP8

but it's clearly being used by 2 male characters who know and like each other- the joke/ point being that their friendship is strong enough that they can use it without either of them being hurt or offended. There's still misogyny there are these characters know full well the effect and meaning is completely different if they used it about a woman- which of course is part of "the joke"

Disclaimer- I don't find Gavin and Stacey funny.

Succinct and accurate!

And in all cases, saying it is equivalent to waving a flag emblazoned with "I am a spiteful misogynist".

Good grief OP. Is this the same charmer (your hopefully by now ex lodger) who makes vile comments about your gf ? If it's not, do you think you might need a quick review of the type of males you are spending time with?
Life is far too short to spend time and energy on misogynistic bellends.

It's a term of abuse and contempt deployed against women, including by other women. I wish they wouldn't.

“Fuckboi” is roughly a male equivalent, isn't it? That is a relatively new term of course. I'm not defending "slag" btw.

In Australia when I was growing up lo these many years ago, skag was also the word for spit - noun and verb - so calling someone a slag was equivalent to calling them spittle on the ground. 😕

Men (and women tbh): "If she's slept with 10 different men she's a LOOSE slag."

Also Men: As long as she sleeps with the same man it doesn't matter if they do it 100000x. She'll never be a loose slag.

Slag is just a term to make people feel shitty about having casual sex or more than one sexual partner. Traditionally aimed at women but definitely noticed shift and it gets applied to both men and women.

Spot on

It's sexist.
Even if it became used equally about men and women, which it isn't, it would still be rude and judgemental.
Can't think of a good reason why anyone would use it.

Of course its sexist and your explanation to step daughter is spot on

This.

Being Northern it just reminds me of Viz comic and the Fat Slags (which of course now makes me cringe in horror!)