Here is my 100% Achievement Guide for Afterparty!
So throughout the game, now and again Lola and Milo will pop up with swear words in their dialogue options. The obvious ones.. F.. Ahole.. Dhead ETC.
Obviously, everytime you see a swear word, make sure to choose it. As long as you are purporsefully looking out for swears, you will get this achievement before you go to Satans house for the "Final" Time (When actually Wormhorn appears and splits milo and lola up.
Another trick is, every bar you enter, make you sure you have a drink with you, because when you talk to people, you can sip a drink and a third dialogue option will appear and sometimes will have swear words.
Or if your impatient, you can use Jinsokus guide (Above this one) and get Lynda a Black Death drink and getting her to say Damned until it pops.
Either way, hope this helps!