Meaning of 大概 in「ボクも大概だ」?

Question

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?

Answer 1

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」

Answer 2

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.