Usage of "donde la espalda cambia de nombre"

Question

In this answer to this previous question of mine, the answerer used the phrase

Antonio se hirió donde la espalda cambia de nombre.

as an example of a milder version of

Antonio se hirió en el culo

I'd never seen "donde la espalda..." before and it made me chuckle. However I'd like to understand its exact place in on the social usage scale.

My questions:

1. Am I right in thinking that the meaning of the expression "donde la espalda cambia de nombre" is the approximate Spanish equivalent of the English expression "where the sun doesn't shine"? (Seems pretty obvious, but I'd better check to be sure.)

2. How scandalous is it to use that expression? Would it cause great offense in anything other than very friendly, informal company? The English equivalent is fairly tame.

Answer 1

1. That's exactly what it means.

2. Actually it isn't that offensive nor gross as you are thinking, it's used kinda softly on Radio and T.V. (at least in Colombia and Peru) as a way to means what it means.