I’ll go first: r/kitty. One of the hundred grillion cat subs back on Reddit, the culture in this one was you posted a cat picture, and the only word allowed in the title or in any comments or replies was “Kitty.”
Someone is using that subreddit for covert communications, I just know it. Either on the level of “if u/PM_me_your_nostrils posts an orange cat, we attack at dawn!” or there’s some steganography going on with the pictures, but that subreddit was too stupid to be as active as it was.
If you haven’t heard, there is a theory that the Frozen movies exist solely to make sure if you google disney frozen or any combination of that you are shown movie stuff instead of stories of Walt Disney being cryogenically frozen so he can live in the future.