About 20 years ago, some one strung cheese-wire just inside the entrance to an underpass near my parents' house. Problem was, the 'cycle track' wasn't only for bicycles, and the first person to hit it was on a 50cc moped. Fortunately they were below-average height, and it hit their visor instead of their throat.
Weirdly, I could almost understand that a seriously unhinged individual might set up something like that and then hide to watch the results - but I don't get why you'd go to the effort of setting it up, then just walk off with no concern about the consequences at all?