I don't see what the kid did that's so stupid. It's an obvious joke, & he went out of his way to identify it as such. People make jokes. Sometimes jokes are offensive. Since when is that "stupid"?
The comments are really irritating me. They don't seem to get this idea of "disproportionate retribution." If the police investigated the report, they should have seen that it was an obvious joke, by a person with no signs of violence. Call him up, warn him about being careful with wisecracks like that, & call it a day. What happens to freedom of speech if satirical comments are prosecutable "threats of terrorism"?