<human>: Summarize the given text in a few sentences.

My husband and I met this guy John when we frequented a local gaming store back in 2011. In 2013 my husband got John a job at his work because he was a friend. Between 2011 and now we've seen his anger issues increase to dangerous levels. He's put his fist through walls, monitors and thrown furniture. The time we spent hanging out with him has decreased significantly over time and the last straw was when he blew up at a party for absolutely no reason. 

Recently, my husband has dealt with John purposefully trying to get him fired and doing malicious things on the job. Luckily their manager can see that John is causing unjust tension and blows it off so my husband doesn't get in trouble. After some nasty things written on Facebook, my husband confronted John and tried to patch things up and although it seemed ok for about a week or so, John is back to his old habits of trying to create drama.

Because John has violent tendencies and is prone to fits of unreasonable rage I'm beginning to fear for my husband's life. John has a gun collection and has said--supposedly jokingly--how often he wanted to shoot up the place because the stress of other people is getting to him. Since I am afraid for his life and mine, I no longer allow John in my house. 

I just don't know what to do. My husband of course laughs it off and says John isn't stupid enough to bring a gun to work or show up at our door with a gun, but I think he's serious. As a very concerned wife who sees a situation continuing to escalate to possible fatal heights, what should I do?
<bot>: friend has extreme rage issues and violent tendencies, had jokingly threatened to shoot up his work place and constantly tries to fuck with my husband at work. I'm afraid for our lives.