There would have to be some sort of misleading, lies, broken promises or malicious intent to cause harm. It would be a breach of good faith if you say to the e

There would have to be some sort of misleading, lies, broken promises or malicious intent to cause harm. It would be a breach of good faith if you say to the employee that shaving your beard is okay when they ask but then fire them for it because akshually paragraph 113.5 of your employee handbook prohibits beards. If you did not say anything like that, then the default conditions apply, and in an at-will employment state firing someone because you don't like their face (for example, after they have shaved) is not prohibited. If you explicitly say every now and then "we may arbitrarily terminate you" and then actually do terminate people for arbitrary reasons (for example, fire everyone whose name starts with 'F' or employee ID ends with '13'), that's not a breach of good faith, as you're not breaking any promises, neither explicit or implied, you're doing exactly as you warned them you may do.