One more colorful slang term I gleaned from the British movie I recently watched is slag. In the movie, it was used in curses like, "Fuck-ing dogs! Slags." "Right slag, that one."
Now I know via dictionaries that slag means "a loose, promiscuous woman." But there are multiple slang terms for such a woman in American English that have varying levels of vulgarity — here's how I would rank a couple of them, from least to greatest in vulgarity:
skank < slut < ho < bitch < cunt
So where does slag fit on this spectrum? Of course, I imagine you'd never hear it on proper television, but is slag barely elided over when someone goofs and says it, kind of how the word bitch is in American English? Or is it a word that a rough group of friends might use around each other casually, sort of how the word motherfucker is in American English, and apparently cunt is in British English? Or perhaps slag is a word that one should prepare for a fight over if one uses it, like cunt in American English?
Best Answer
Before getting to the main answer, a few points that may be interesting to you (though I realise they're not actually part of your question!):
On to the main question: it's probably worth distinguishing between the degrees of offensiveness of (abusing terminology slightly) use and mention of the words: that is, some words can be happily used in polite society, but one would be highly offended to be called one - whereas with some words merely saying the word (regardless of who it is applied to) is offensive in of itself.
Having drawn that distinction: mention of the word slag - while it's clearly to be avoided when on one's best behaviour - is unlikely to cause much offence; that would put it on a roughly similar level to slut or perhaps skank.
However, using the word slag to describe someone would be a good way to start a fight. It is probably at a similar level to slut: perhaps slightly more offensive, if only because slutty/sluttish can refer to general demeanour (in dress, speech) - and indeed can occasionally merely mean "untidy, slovenly" with no sexual connotation - whereas slag is unambiguously referring to sexual behaviour.
It's worth mentioning the word is used a lot in comedy - perhaps the earliest was in the comic Viz (decidedly not a comic for children, and never noted for its reverence); here's an example in Harry Enfield's sketch show; and more recently in Gavin and Stacey. (Using the word for men isn't common except in reference to this show!). You can probably see - especially from this last example - that this word can be thrown around among close friends in a humorous way - but I would strongly advise against doing so unless you're very sure of what you're doing, since the line between banter and offence is a very narrow one at times :)