*Note: this post will contain rude words.
It seems this question pops up on writing fora over and over and over....Can I swear in my books?
The short answer is yes, yes you fucking can.
The long answer is, well, it depends. You can, of course, but should you and when is it appropriate?
First of course you need to consider your audience. If you're writing an early reader picture book, rude words are probably not going to help your quest for publication. However, if you're an adult writing for adults then you can.
Is it usual/common in the genre you write in? Dark, gritty fantasy? Yup. High, Tolkienesque fantasy? Not as much, though it's still there. Cosy, Miss Marple type whodunnits, no, not really.
Do you need/want to? Well, not every book is going to need swears. Because personally I think it's all going to boil down to: Would this character swear in this situation? If you're writing a brutal battle scene with lots of roughty toughty soldiers, or a riot where firebombs are going off all over the place, then if someone gets their arm blown off, then writing 'Oh my golly gosh, that really hurt' as dialogue...well it's going to look fairly silly. Unless you've set them up to be the sort of character that never, ever, ever uses naughty words.
Because what swears someone uses (or chooses not to use) is a part of characterisation. Think about it - I bet not everyone you know swears (or doesn't) in quite the same way.
You'd be hard pushed to get more than a 'damn' out of my mother, mainly because she was taught as a kid that ladies don't swear.
I'd be very surprised if my local vicar used anything blasphemous (though non-religious words are, it seems, fair game for him. Mostly)
I know a chap who seemingly can't finish a sentence without at least one swear - it's a kind of punctuation.
I have a tendency to string lots of swears together, then end on one that always makes me laugh. Either that, or I make some up. I would not, however, dream of saying anything worse than 'damn' in front of my mother, or the vicar. Because I'm polite like that. And my Mum would give me a clip round the ear.
One of my characters never swears - he's too buttoned up to let go in such a way.
Another of my characters swears because it pisses off the people around him, and he likes doing that.
So, if it's reasonable in your genre/for the audience you're going for, and your character is the kind that might swear in this situation, then probably they should fucking well swear. Get inventive. How does your character react to swear-inducing situations? Or, indeed, when confronted with someone they won't swear in front of, or is somewhere where swearing is going to drop them in a world of shit? Do they use euphemisms? Do they clamp their mouth shut and let steam come out of their ears rather than offend? Or do they just swear anyway?
You may have to deal with those who say that swearing is a sign of a limited vocabulary or a poor education etc etc *yawn* To those people, I give you Stephen Fry on the joys of swearing.
Because if Stephen's got a limited vocabulary, I'm a fucking tosspot.