emperor's new clothes?

[Lazerz]

How do you even get this acheivment, i just got a empire and achievment hunting but i dont understand how to get this?

[76561198036714142]

There are religions that let people be a pervert. And some events give you the pervert secret. Perverts are naked if you become one as emporer you will unlock this. If you are an emporer and you have a reformed religion there will spread heresies that have those characteristics from time to time when your ferver is low.
If you switch to that new religion only for that archievment make sure you have enough piety to switch back or you might get trouble ;)

[Tao]

All I did to get the achievement was play as West Francia and declare war on Lotharingia as soon as the game starts. I went with the medicine focus in the learning lifestyle tree so that I get the small health boost. The ruler will die really soon so it is best to take that focus so you can secure your succession. When you annex Lotharingia, ally with the Byzentines or someone like that so you will be fine when an independence faction rises up. Save your money and form Francia. Once you do that, marry an adamite and convert to the adamite religion. You will be naked and own an empire.

It was the easiest achievement of my life.

[Elenjo [Ger]]

there are several tenets in Religions where you become naked, the easiest way to get it (without playing that savegame again) start with Byzanz and Convert to Adamite, or if you make a campaign for yourself, then create a new Religion of some kind and make your tenets like : Natural Primitivism.
but as a tip, if you make a new religion out of a Preset Big one then get the land of the ReligionLeader first because he would send Crusades to take back some countrys from you.