Not necessarily a sign of widespread social media surveillance, but you still have to wonder how the state of Delaware's Attorney General's office managed to come across a comment referring to some St. Patrick's Day-related NSFWing, much less pursue one unlucky commenter who made a joke about one of the participants being his "sister."
Here's a link to the photo which kicked off the unlikely chain of events. It depicts two green-clad people, presumably of consenting age, expressing their love in a physical manner. Needless to say, probably, very definitely NSFW.
Redditor un1cornbl00d received notice from Reddit that the Delaware DOJ had served a subpoena demanding the platform turn over his personal information, along with "all posts, responses and their content" related to the original submission. (Found here, with comments now deleted).