The Outer Worlds: Spacer's Choice Edition

The achievement is unlocked during the Prince of Tossball main story mission. This is the mission where you investigate Bertie as a suspect. It is missable. First, this is not a mandatory mission to complete the story and becomes unavailable once you progress past a certain point. Second, you must have at least one companion with you. Finally, you must use the right dialog choices first to trigger a companion to act as the bad cop and second to keep that companion true to the bad cop role. Doing so, pops the achievement.

Make sure you take at least one companion with you. I recommend Felix and Parvati because they increase your persuasion and your lockpicking--skills that are especially useful during this DLC. However, Ellie is the easiest for this achievement because she doesn't need coaxing to be a bad cop.

The Prince of Tossball main story mission takes you to Piraeus Spaceport where you are able to track down "Black Hole" Bertie and interrogate him. Before talking to Bertie, make an insurance save. If playing on supernova, pop out of the spaceport and back in to create an autosave (Bertie is not far from the entrance/exit to the spaceport so you loose little time). During the questioning, the options do not matter but it's best to be as skeptical as possible. After several questions, Bertie will say, "I don’t wanna tell you. I’ll get in trouble."

This is the trigger that will lead to the option of choosing a companion to be a bad cop. If you've followed the suggestion to include Parvati and Felix, you will have the following two dialog choices along with a couple of others:
--What do you think, Parvati? Up for a little "good inspector, bad inspector"?
--Okay, Felix, you're bad inspector. Just like in the serials.

Choose a dialog option that makes the companion a bad inspector. If you pick someone other than Ellie, the companion will be somewhat reticent. In the above example, Parvati is a nice person and doesn't like to be a bad inspector. Felix is a fan of Bertie and doesn't want to be hard on him. Do not let the companion stop, even if asked. Encourage the companion to continue as the bad inspector and make sure you do not pick a dialog option that has you interrupt the companion.

If the companion does not conclude the bad cop questioning, the achievement will not pop. Conversely, you unlock the achievement when the companion successfully completes the bad cop questioning. If the conversation finishes without the achievement popping, make note of what aborted the bad cop routine, load the insurance save and make choices that allow the companion to finish the bad cop act.