[withinboredom]

You don't need a reason to fire someone in the most of the US (AFAIK). You can just say that they walked in with a red shirt and you don't like red shirts. As long as the reasoning isn't because they are in a protected class, you can pick whatever reason you want.

[pcthrowaway]

Firing someone "because they walked in with a red shirt" would do damage to your company's reputation, and call into question the competence of your management team.

And you can still get sued.

[withinboredom]

I mean. You can get sued for wearing a red shirt. It would probably get tossed out in ten seconds (unless the judge just wants some entertainment). But you can sue anyone for anything. You can do tens of millions of dollars to a company, get fired for it, and sue them. Nothing is stopping you.

Secondly, no one is going to give a shit why you fired someone except the person you fired (if you even told them why), and HR. In fact, most companies don’t even give managers firing authority, but if you are the owner/CEO or someone who does have that authority, it’s possible even HR doesn’t know the reason. That person is just fired.