It really depends how much expression you wish to add to your conversation, and how bad you are prepared to go with your language!
'Shit!' is very common slang but would be inappropriate in many situations - in fact, all situations other than social ones with friends. A more generally acceptable expression would be 'Damn!'
One of the most common swear words is 'Fuck!' which you hear all the time and especially in films. This is a worse swear word than 'Shit!' and should be used only when with friends as it may offend some people.
Generally when a non native speaker tries to use expletives, it sounds strange and unnatural to the native ear, so the advice is not to use any expletive and find softer and more acceptable words: for example: 'Oh bother! 'Sugar!' 'Oh my god,' 'Jesus!' but also remember, any religious word used in this way may also offend some people.
The use of curse words can be offensive, even to a close friend, if they aren't used to hearing someone curse. Furthermore, it can sometimes come off as childish. I think the most acceptable, yet also vulgar way of saying this, would be to say "Crap!"
If you are really pissed off, some people would say, "Fuck!" However, it might seem offensive to some people.
The use of expletives like the word "shit" is never considered proper English. It can be very offensive as it literally refers to human excrement and is a very vulgar expression. Individuals who frequently use expletives demonstrate a strong lack of vocabulary. Hence, it's better to increase your vocabulary and use terms specifically relating to your situation. For example, if one is simply making an exclamation: he could say that's horrible (or other similar expression). A more slang, but nonoffensive expression would be "oh man!" It simply indicates that you are upset about a situation.
The word 'damn' functions as a verb, an adjective and as an exclamation. In in this case, it has been used as an exclamation expressing anger or frustration. If you are with a friend and suddenly, something happens that you did not expect would happen, you may say:
Damn! I didn't think that this would happen.
or
Dam-nit! This is not what I expected!
or
I didn't expect this. Shit, man
Please note that some people who are not your friends may regard the last line as unacceptable.
この'damn'は動詞、形容詞又は感嘆詞として機能します。
この場合、感嘆詞として怒りや不満など表しています。
友達と一緒にいる状況で、何か予期せぬことが急に起こったとします、あなたは次のように言うことが出来ます。
"Damn! I didn't think that this would happen."
（くそっ！こんな事起こると思わなかった！）
又は
"Dam-nit! This is not what I expected!"
（くそっ！こんな事予想してなかった！）
又は
"I didn't expect this. Shit, man"
（想像してなかったこれ。くそっ！）
最後の表現は友達ではない人に使うと許されない場合もあることに注意しましょう。
さまざまな言葉がありますが、shit や damn it は比較的良く使われると思います。
もちろん、フォーマルな場で使うのは好ましくないので注意してください。
例：
Shit, I forgot my keys.
くそ、鍵を忘れてきたみたいだ。
Damn it, I made a mistake.
くそ、間違えた。
お役に立てればうれしいです。
・Oh, darn.
うわ、くそ。
darn は shit などよりはマイルドな英語表現です。
oh, darn のように言うことも多いです。
例：
Oh, darn. Now I've done it.
うわ、くそ。やっちまった。
ご質問ありがとうございました。
また何かございましたらいつでもご質問ください。
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