Between "Decaying Pocketwatch" and "Drinking Gag" is "Designer Handbag"
To get it you need to interact with "Black Shrine" in the laboratory of "Errant Signal" with an adventurer with "Bimbo quirks >= 2"
Viewing post in Ero Dungeons [Complete] comments
First you need to get four "Black Visors".
You can get them by interacting with "Black Shrine" if "Bimbo quirks <= 2".
"Black Visors" prevents "Bimbo tokens" and "Bimbo quirks".
Now all that's left is to advance through the dungeon until you find "Errant Signal", defeat it and find the exit.
Personally what I did was:
-Enter the dungeon, go north, go north, go west, go south, go south, go south. There is a "Black Shrine" there. Now go east and open the shortcut at the beginning. Go in and out of the dungeon until you get 4 "Black Visors".
- Now that I can prevent "Bimbo quirks" I erased them from the adventurers, formed a hyper-offensive team that defeated common enemies in 1 to 2 turns and advanced without problems until I found the "Errant Signal" in the labyrinth.