Ah, the question many of us like to ask. And a valid one, I'll give you that.
Still, I don't know if we often get the answer right. This question is usually asked when addressing some sort of strategic or creative decision, e.g. for a brand, so that we can properly measure the pros and cons of any idea.
The answer to this is usually a crisis on a social platform. A PR backlash. A misinterpretation of our message by our target market. I do, however, think there's a much worse option.
No resonance. No feedback whatsoever. Not even a single "boo". That moment when you know how many people saw your stunt, and not even one bothered to say a thing worth noting.
All things considered, the worst thing that can happen is nothing.
P.S.: Of course this doesn't mean that a PR crisis is a good thing. But the ability to reflect and choose between the bad and the worst option is actually a great mental exercise.