From The Annals Of Dumb Criminals
Lexington contributes a gem:
[Major Marty Sumner] was describing a period when the police in High Point were trying to figure out which local youths belonged to which street gangs and which gangs were involved in which types of crime. It turned out that one of their most valuable sources of information was the gangs' own Facebook pages. Some gangbangers had posted pictures of themselves posing with guns, showing off their gang insignia and bragging about the money they were making. They also posted messages to each other, making it farcically simple for the police to figure out who was associated with whom.