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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Some Slang

These aren't really bad words, just some relatively common slang phrases. Some of them might sound foolish if used with a professor.

pumped
興奮してる

Example:
Are you pumped about the concert tomorrow?
明日のコンサートを興奮してるかい？

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wasted
よっぱらった

Example:
I got seriously wasted last night at the party.
昨日のパーティーでまじよっぱらったな。

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pooped
疲れた

Example:
Man I'm pooped after carrying all those things.
ハッ、あんなものを運んで疲れた。

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wicked
凄い

Example:
That car can fly? Wicked!
あの車が飛べるの？凄い！

Comment:
I might not have gotten the usage for this word correctly, since it's more common among British than Americans.

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pissed
怒ってる

Example:
He got so pissed when I threw that egg at him.
俺はあの卵を投げたから、あいつ本間に怒ったぞ。