Failed

owned
やられた

Example:
I got owned last night on Call of Duty.
昨日コール・オブ・デューティでやられたよ。

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Comment:
This can also be pronounced pwned, at least when gaming.

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schooled
やられた

Example:
I got schooled by that test yesterday.
昨日の試験にやられたわ。

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epic fail
大失敗

Example:
Making Haiti pay France so much for independence was an epic fail.
ハイチをフランスにあんなに払わせるのは大失敗だった。

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Something else

something else
他の何か

Example:
I'm bored, let's do something else.
つまんない、他の何かしようよ。

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something else
すごいもの

Example:
Wow, that car really is something else.
うわー、あの車は本当にすごいよね。

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Comment:
Compared to the more traditional translation of すごい as awesome, something else is probably softer, or more subtle.

Honesty

You have my word.
約束だ。

Example:
A: Are you really going to buy that for me?
B: You have my word.

A: 本当に買ってくれんのか。
B: 約束だよ。

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open
あからさまな

Example:
I'm always open about my feelings. It's simpler than hiding them.
いつも気持ちに対してあからさまだよ。隠すより簡単だし。

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Honesty is the best policy.
正直は最善の策

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Avoid

plague
ペスト

Example:
A plague in Europe killed around half of its population.
ヨーロッパのペストは人口の半分ぐらい殺した。

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avoid like the plague
～を徹底的に避ける

Example:
Ever since she started her diet, she's been avoiding sweets like the plague.
ダイエットを初めてから甘いものを疫病のように避けてる。

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Paper vs Reality

on paper
書類上

turn out well
うまくいく

Example:
The idea looked good on paper, but it didn't turn out so well in the end.
書類上ではいいアイディアだったのに、結局うまくいかなかったな。

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count
重要である

Example:
It's what's on the inside that counts.
大切なのは中身です。

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Comment:
That's why you can't judge a book by its cover.

Uphill Battle

uphill battle
苦しい戦い

Example:
It looks like peace in the Middle East is going to be an uphill battle.
中東での平和が困難な闘いになりそうだな。

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Comment:
The world would be a better place if only it wasn't so hard...

Rules

follow the rules
規則に従う

Example:
If you don't follow the rules, someone'll get hurt.
ルールを守らないと誰かがけがするよ。

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play by the rules
フェアプレーする

Example:
The game's no fun if you don't play by the rules.
フェアプレーしないと楽しくないよ。

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Comment:
You can use this expression even when it's not a game, in which case it means the same as follow the rules.

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bend the rules
規則を曲げる

Example:
I bend the rules sometimes when I have to.
必要な時はルールを曲げる。

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break the rules
規則を破る

Example:
Rules are meant to be broken.
ルールは破られるためにある。

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Comment:
No they're not, let's all follow the rules like good people...