I'm also confused by the translation of the French idiom.

But then I'm also confused by the idiom itself: I think initially it's "j'm'en branle", "I'm wanking off of it".

Then the hit my balls part should be similar to "beat your meat".

Hence my proposed translation: I'm beating my balls off of it.

And yes it's quite rude language in French too, that I'm sure!

But... There's more !

Like many foul language in French, it can be decorated and escalated, even if it deteriorates the meaning. For the same idiom, some variations specify what you're using to beat your balls: With a tart server: j'm'en bats les couilles avec une pelle à tarte With a french window: j'm'en bats les couilles avec une porte fenêtre

If you're the proud owner of a vagina you would instead say: "j'm'en bats les steaks". Steak is the same English word but here it refers to your labia. Then I guess the same variations as above can be applied.