The first character starts by saying their view on a situation, the second then replies with an opinion that is viewed as ridiculous and unbelievable by the first. This first character then replies:
ボクも大概だけどキミも相当だな
In the subtitles this is translated as:
I have issues, but you're just as bad.
While I understand the translation for the second half, 「ボクも大概だ」 doesn't seem to make sense.「大概」 meaning 'generally' or 'mostly', is it akin to the phrase 'I'm not all there' in English?
Dictionaries say the basic meaning of 大概 is something like "moderate", "overview", "almost all", "usually", etc.
- 大概のところでやめる / 大概にする to stop before going too far; not to go to extremes
- この店で大概の品物は見つかる。 Almost all items are found in this shop.
- 土曜日は大概会社にいる。 I am usually at my office on Saturdays.
However noun + も + 大概だ means something different. It's a way of indirectly implying something/someone is equally out of the way, abnormal, extreme, bad, etc. Basically it's interchangeable with noun + も + 相当だ. I don't know if this usage is originally sarcasm or euphemism. For some reason we usually see も used with 大概 in this sense, so you can memorize this as a set phrase.
Examples:
- 日本語は難しいといわれるが、英語も大概だと思う。
- あの部長は怒ってばかりいますけど、部長も大概ですよ。
大辞林 has the corresponding definition:
④ふつうでないこと。はなはだしいこと。
To my surprise, デジタル大辞泉 does not explain this usage at least directly.
By the way, the sentence in question can be rephrased as ボクもボクだけどキミもキミだな. See: Meaning of pattern 「XがXなら、YもYだ」
大概だ is a kind of idiomatic phrase; perhaps this 大概 is used in the sense of "mostly" or "to a great extent" and 大概だ is used usually in the sense of "being mostly/very bad," "shoddy" or "ordinary/dime-a-dozen." Anyway it has a different meaning from its literal definition and has a negative nuance.
ボクも大概(問題がある)だけどwith the問題があるomitted. – rurouniwallace May 26 '17 at 19:45