I'm French too and have never heard of that one. Also, "I slap my balls on it" is probably the translation of "je m'en bats les coulles", but a better translat

I'm French too and have never heard of that one. Also, "I slap my balls on it" is probably the translation of "je m'en bats les coulles", but a better translation would be "I slap my balls with it". It is sometimes shortened as "j'm'en balec" or even just "balec".