This trophy can be unlocked after you go to Canada and unlock Nagasaki. The first step is to befriend the underpants gnome. You can do this very easily by completing the gnome side quests to find 5 underwear. The quest is available right after you finish day 2 and the main quest that night. If you explore everyones house you’ll find the underpants very quickly. Go back and talk with the gnome and you’ll get the first part done.
The next part is in the sewers. After unlocking Nagasaki go down into the sewers and try to get to the emergency exit area. If you go through the “emergency exit door” it leads you to a cave with bats and a rock you need to use Nagasaki to break. Once your through the rock just talk to the crab on the other side and the trophy will pop.