Slang, of course, is part of dialogue, though it can also be found in prose. But slang has dangers.
Do you have a 100% command of the slang of the period and of the geography you are writing in?
Do you understand the slang? As an example, we have a discussion at present on the Literary Merit forum about the use of a simple word 'skinning' deployed in When Shadows Pass. Does it mean stripping naked, or pulling pack the foreskin, or does it have some other meaning? And the answer is unclear, and may even depend on the part of a nation one is in. The author knows it to have been used within his experience and in that geography in the way he uses it. Others cast doubt.
Slang will date your work. While your work may be set in a time period, that does not, of itself, 'date' it. Slang is an item of the current time. Prior era slang starts to become unreadable.
As author you have full control. Use what is important, what adds value to the plot, and leave the rest aside. Otherwise you risk losing a proportion of your readers as they trip over the landmine you had no need to leave in their path.
American Alex makes this point very clearly below, though he cites some apparently British slang I have not yet come across.
I'm reading through a story which is set somewhere in a northern rural location in the US. I'm up to chapter 3, and already the word "bloody" has been used twice. Americans DO NOT use this word, unless they are trying to sound stereotypically British. Never in the US, and rarely even in Canada. Using British vernacular in an "American" story is improper, and should be avoided.
Certain other "Britishisms" should also be avoided when trying to sound like an American. Words like "pram", "roundabout", "petrol" and "boffin", exclamations such as "brilliant", "oi" and "cor" are also never used in American dialogue. Certain 'Northern' or Celtic terms like "bairn", or "ceilidh" will confuse most Americans. Certain grammatical forms like "the caller has hung up" or "in hospital" are also distinctly British, and not American. Certain loan words from French, like "aubergine", "abbatoir", "fete" or "palais" likewise are never used in Amercan vernacular.
Going further, there are certain terms which would confuse nearly any American. "Lollipop lady", "fruit machine", "rock trousers", and "Hoxton bonnet" come to mind, mostly because I've just recently learned these expressions. British standard spellings also sometime differ; sometimes slightly, as in center/centre, to the more extreme like in jail/gaol. A quick way to make these sort of issues minimal would be to set your spell-checker to American standard English, if only to check your accuracy.
This table shows some common and less common variants on British slang.
|Slang Word or Expression||Meaning|
|camp||having a gay manner|
|faggy||gay in apparel/appearance|
|hanky-panky||provocative sexual behaviour|
|prissy||affectedly prim and fussy|
|soixante-neuf (French)||sixty nine|
|a bag-head||a silly twit or idiot|
|a blast||bloody good fun|
|a blue fit||an annoyed angry tantrum|
|a dork||an awkward misfit|
|a fucktard||an obnoxious person|
|a fuckwit||a grossly stupid person|
|a goose||a comically silly person|
|a hoot||good fun|
|a nincompoop||a vacuous twit|
|a poppet/popsicle||an endearing youngster|
|a prick||a very annoying person|
|a scorcher||someone hot and sexy|
|a wanker||incompetent stupid person|
|a wuss||a cowardly wimp|
|a yob/yobo||a rude aggressive person|
|yay||woohoo/a cheering yes|
|yikes!||exclaiming sudden surprise|
|yo!||exclaiming amused surprise|
|yolo||you only live once|
|wavey||high in mood/intoxication|
|whopping||oversized/larger than normal|