Me, taking a coding class in uni:
Purposely cramping everything in as few lines as possible, making the code barely readable, just to screw with the guy who had to correct this mess.
In my defence, the assignment they gave us was garbage. The task descriptions were often ambiguous or even contradictory to what actually was the case ("The InputStream will contain a string of csv data, each element starts in the next line" -> was a malformed single line string) and the automated tests they wrote to check our output where either completely unhelpful because of their meaningless error messages, or sometimes even plain wrong, telling us our output was wrong, even though it definitely wasn't.