My 8th grade son has had some similar issues when angry or upset. Most of it has been minor and his teachers are pretty low key about it. The only major issue was when he said he wanted to burn the school down because he was upset about a penalty being placed upon him. Thankfully the school is small and all the staff know him well and his immediate reaction after saying it was to apologize and swear he didn’t mean it so after a consult between the principal, counselor and psychologist all decided it was an outburst not a threat so it did not escalate. I know that’s probably not helpful advice, but wanted you to know you’re not alone. I have had several talks with him about using these kinds of words and how they could end up getting him expelled or in juvenile detention because people take threats very seriously. He is also buddies with the School police officer who has explaied the same issues and potential consequences to my son so I think having someone of authority besides myself or teaching/admin staff talk to him about it has made an impact.