What comes to mind when you think of customers getting employees fired?

Depends on what the employee did and if it is founded. I usually view the majority of your average retail customer to be an entitled piece of garbage that can't be told the word no lest their world be torn asunder. The concept of the customer is always right had lead us to entitled lazy people that think if they moan loud enough they'll get what they want, even if it costs someone their job. I instead counter with the customer should always be treated with respect, until that respect is not returned.

Honestly, I think of the spiteful individuals who couldn't get their way even if they were in the wrong so they take it out on anyone who gets in their way. The most common examples are the retail scammers who get caught in the act and threaten to call corporate. Hell, I worked at an ice cream parlor when I was younger and I had a customer literally throw a napkin dispenser at the back of my head because I served my customer before the employee who was filling his order served him.

Sometimes the customer can be awfully petty and the belief that "the customer is always right" has only emboldened people spiteful people like that.

Egregious unprofessional behavior. Such as, personal attacks on the customer by the employee.