On the wall to the left of the fireplace in The Lodge, there is a fish on the wall you can interact with. It will tell a joke and spit out a few guns.
You can use it once everytime you go into The Lodge.
(See Edit 2 below) You can see in the screenshot the fish is right inside my reticle.
Edit: As stated in the comments below as well as finding a few myself, there are a few in other location around the game but this one seems the easiest to farm.
EDIT 2: I haven't played the game since this DLC so this is info is from users in the comments. Shout out to AngryCalf452023 and FivePartTrilogy for the helpful comments.
With the addition of Mayhem 2.0, you can re-load your game quicker and the fish will tell you a new joke each re-load. Set the Mayhem level to 10 and just re-roll the modifiers by hitting X on the Mayhem settings tab. That way any loot that the fish spits out has a better chance of being something actually useful.