This seems like nothing more than vandalism to me and might be worth 40 hours of community service time at the maximum. To construe this as some kind of terrorist threat required someone to perform some mental gymnastics and was nothing more than an exercise in creative stupidity. It seems that an awful lot of stupid makes it in the news lately. I think the USA is in the middle of a stupidity epidemic!
With terroristic threat laws, the suspicious talk itself is the crime, not just evidence of plans for one. The cops can arrest for the threat charge and investigate the possible underlying violent scheme later. Meanwhile, the accused is not simply enduring the inconvenience of a police inquiry. He is locked up. Even if he is ultimately acquitted or charges are dropped, months of lost liberty is too high a price for using gauche language or failing to understand his audience’s sensitivities. It’s too high a price when police could have investigated the old-fashioned way.
LINK: https://www.techdirt.com/articles/20141106/19035829074/student-facing-terroristic-threat-charges-after-decorating-high-school-bathroom-with-laughable-satanic-graffiti.shtml