When you no longer find "Office Space" funny, but instead it just makes you mad, that's a red flag.
This one is courtesy of a coworker in 2004, when I worked at a bank. 😃
#RedFlagsAtWork

That employer tried to get itself some financial leeway by switching from paying salary current to paying in arrears. Which is to say that they changed from paying our salaries for a pay period at the end of that same pay period to, instead, paying at the end of the next pay period. To soften the blow, they payed us two-thirds salary for three pay periods.
I would later learn that the two-thirds compromise had been hard won by angry managers who cared for their people and had pushed back hard.
#RedFlagsAtWork

As that particular employer's finances got worse, they hired a comptroller. He only lasted a few months. As far as I remember, there was no talk of finding a replacement.
#RedFlagsAtWork

At that same very small company, All of management had bought stock. I had been there for almost five years without ever getting a raise or a bonus when my manager stopped eating lunch out and started keeping sandwich bread and peanut butter and jelly in her desk drawer. All the managers were in not so great moods, actually. I didn't understand at the time, but I would later learn that the company was not paying managers their salaries.
#RedFlagsAtWork

At another job, a very small company, the COO was giving a customer a tour of our office and popped into my office to introduce me. I swear to god he introduced me, "this is Brian. he's a good little programmer". I should have given two weeks notice right then and there. It would have saved me years of stupidity.
#RedFlagsAtWork

Also at that job, I once had a boss who managed by checklists and was only concerned with getting all the details correct. The only feedback he ever offered was the mistakes I had made. Once after a project release, he told me I had done well. I was so sick of his highly specific negative criticism that I was eager for some specific positive criticism, so I asked him to give me an example of what I had done well. He could not. He actually stammered briefly then allowed merely that I hadn't made any mistakes. He was visibly confused why I was not grateful.
#RedFlagsAtWork