I doubt the affirmation that "PD" means "Par Derriere" (From Behind). It's a very frequent insult in french, and I never heard that explanation.

It's pronounced "Pédé" in French, and should probably come from "Pédéraste", which share the same etymological roots with pedophile :

"Pedo" in ancient Greek meaning "boy" or child. So pedophile means "loving young boy" and "pédéraste" has the same meaning and was by extension given to gay male as an insult.

And latter on was shortened to "Pédé" then "PD".

The "From Behind" may be the way those people understood the word in this part of the world.

Nice read either way.