Immediately after finishing the darkroom, you will be in a jail cell talking to a lawyer named Anu.
After like 2 dialogue choices, she will begin listing off every crime you've been accused of. To unlock this achievement, you need to respond to every one with "It was dark and I'd been drinking!"
It will pop after the last time you get that option (like 5 or 6 times).
You should have a save before making the decision in the dark room to go to Dick or Lemma & Erin for their respective achievements anyway on your playthrough. So, if you miss this, load that save and make the other choice and take a swing at snagging this again.