Entity

I released some kind of noncorporeal SCP-style horror. This entity was being contained in a government facility which seemed to be a mixture of datacenter, power plant, and research center. I don't remember exactly why I released the entity, but it might have been malicious on my part. The main effect of the entity was to create pervasive glitches in reality having to do with most kinds of communication channel. Any kind of symbolic communication would be changed randomly, in ways that mostly maintained the pragmatics of the message while destroying epistemic content. In other words, the more a property of the message matters to you, the more likely it is to be preserved by the entity; but unimportant aspects of the message get a lot of noise injected. The communication glitches are inserted into the brain as well, resulting in an altered state of consciousness for everyone. However, spoken language was only mildly effected by the glitches (as compared to written language).

An additional effect of the entity which was not so obvious was that any symbolic act involving a symbol for "up" is interpreted as a call for the entity to eat you. Somehow we were able to communicate this to people without getting eaten, though.

Society gradually devolved into a non-functioning post-apocalyptic state due to the difficulty of things running smoothly under the influence of the entity.