Short-hand for a crude and disgusting racist acronym, describing the racial identity of the perpetrator of a crime. Literally, "A N****r Did It."
Person 1: Did the police give a description of the suspect of that drive-by shooting that ended up killing that innocent 9 year-old bystander?
Person 2: Yep, the statement was reported on the evening news.
Person 1: Well, what did they say, who was it?
Person 2: Andi, of course. It's always Andi.
Person 1: I should've known. When is it NOT Andi?