Just be slutty and spread debauchery at every chance you are given, and eventually you'll get the bad ending.
There's also a situation where you find an acolyte outside the temple and you can offer her restrain potion or lust potion. If you give her lust potion it would increase the lust. The same with Rhot, you can later give him certain items that increase/decrease lust. But in most cases, just pick a naughty options.