fired for rumors of insubordinate conversations

I was recently terminated from a new job. I had only worked for them for 5 days. The last day, I got called into the office and the conversation went as follows; word-for-word: "This isn’t going to work. We are going to have to part our ways. There are rumors of insubordinate conversations. As of today you are no longer employed by Gander Mountain. following this my reply was (okay?).
What, if anything can I do about this?

Insubordinate conversations

There does not appear anything you can do as it sounds as if your termination was proper. I am assuming of course that you were a private employee, not a union member, at-will, etc. At-will employment simply means that the employer can lawfully terminate you at any time, with or without a reason. The exception being that the termination can not be on a protected basis such as age, race, etc.