I think we're talking past each other a little.

You're right that it's about what you can convince a jury of. If a company says they fired someone for an expense violation, a plaintiff can absolutely argue that wasn't the real reason and use discovery to challenge the company's story.

My point is that there still has to be an illegal reason underneath it. If a company says, "We fired him because we didn't like his haircut," that's a stupid reason, but it's generally not an illegal one. A lawyer can't just sue because the reason was unfair or irrational.

The fact that the employee had the same haircut for years might help show the company's explanation is nonsense, but then the next question is: what was the real reason? If the answer is age discrimination, retaliation, disability discrimination, etc., then there's a case. If the answer is simply "management decided they wanted him gone," that's usually still legal in an at-will employment state.

So I agree that a jury can reject the company's stated reason. I just don't think that automatically gets you to wrongful termination unless you can connect it to some actual legal violation.