A coworker overheard managers at my place of employment stating they were afraid to fire me in fear I'd "shoot the place up". Would that be considered slander or defamation?
I am giving you a general answer and would need more information before giving you specific advice. I am a Michigan attorney who has handled defamation suits in the past and the information provided pertains to Michigan.
In my opinion this would constitute libel and defamation. The communication from one manager to another might be deemed a privileged communication depending on the facts of your situation. Some defamatory statements are deemed privileged which constitutes a defense to a defamation lawsuit. If your co-worker was not in management the publication of this statement to the coworker constitutes defamation under Michigan law ( assuming there was no other basis to assert a privilege).
Please keep in mind that a defamation suit must be commenced within one year of the date the defamatory communication was published (made) to another person.
If you would like to discuss the matter further please contact me.