As other said, "je m'en bats les couilles" means "I don't give a damn". There are lots of synonyms, I'll use "je m'en fous" because I don't feel like writing couilles 10 times.

The whole sentence comes, in my opinion, from the English phrase "Who cares ?", except in English the negation is the opposite as in French:

• "I don't care" is "je m'en fous" but

• "I care" is actually something like "je (ne) m'en fous pas"

So my guess is that to keep the expression "catchy", the negation was swapped. Instead of asking "Who cares?" as "Is there even one person who gives a damn?", it's more natural to ask "who else doesn't give a damn?", which is basically what the sentence is.

I'm not 100% sure but when I started hearing this expression I immediately thought of "who cares?" because of the similarity, and the swap is actually pretty natural.

As other said, "je m'en bats les couilles" means "I don't give a damn". There are lots of synonyms, I'll use "je m'en fous" because I don't feel like writing couilles 10 times.

The whole sentence (with "Qui ... ?") comes, in my opinion, from the English phrase "Who cares ?", except in English the negation is the opposite as in French:

• "I don't care" is "je m'en fous" but

• "I care" is actually something like "je (ne) m'en fous pas"

So my guess is that to keep the expression "catchy", the negation was swapped. Instead of asking "Who cares?" as "Is there even one person who gives a damn?", it's more natural to ask "who else doesn't give a damn?", which is basically what the sentence is.

I'm not 100% sure but when I started hearing this expression I immediately thought of "who cares?" because of the similarity, and the swap is actually pretty natural.