We've lost 2 workers from my department in the past 3 months for this exact reason.
First one was the manager. He brought an AK in, started mumbling paranoid stuff about the homeless people sleeping outside overnight, then mostly unprovoked threatened to bash the assistants head in. In all fairness the assistant isn't too good in social situations and didn't realize repeating “Calm down man, just calm down” often has the opposite effect haha.
Then management tried sweeping it under the rug, we didn't let them, and he sent a text of him holding the AK threatening the assistant to the store manager. He's been convicted on 4 felony counts (menacing, having a gun as a felon, and 2 counts for illegal mods) and will be out in 5-10.
Next guy got mad about the store manager cutting one of his shifts (because of his own actions, which he acknowledged) and asked us for his schedule so he could come in and kill him. Over text.
No arrest as it wasnt overt, but immediately fired and blaming everyone else but himself.
We work at a grocery store, just get another job if it's that stressful. The job is probably less work and less pay than McDonald's, there's no reason to throw away your life for it. There are a dozen and a half jobs right by us that probably pay better.
Now one guy lost his house, custody of his son, and his freedom for nearly a decade. The other will probably be homeless and has to walk 40 minutes in the opposite directions for groceries now.
This was mostly a rant, but guys get some therapy if you need it. A lot of cities have programs for crisis or low income patients. Don't start threatening coworkers, it's not worth it.