[Lucid:]

To be honest, I don't think it is ever okay to make any comment about that kind of violence, joking or not. The woman was right to report him and the kid deserved to be arrested, to show him that it's not okay to say things like that.

It's similar to the way that therapists are legally obligated to report certain things that their clients say, even though most are taken in complete confidentiality. If there is even the slightest mention or hint of suicide or violence towards others in the person's life, they must be reported to the police. Same goes for this kid. He said he would do it, so kidding or not, he deserves the consequence of being reported to the police and arrested.