9. Commissioner John Kelly
Not to be confused with the other John Kelly of the same series, the Commissioner John Kelly isn't in the slightest a bad character on a technical basis. He has everything that a good contemporary villain should have. He's intelligent, he's somewhat charismatic, he has a motive and actively despises the heroes trying to bring him down. But, controversially, this is what also makes him one of the worst characters in the entire series.
It seems his motivations just don't justify his actions. He'd already beaten Captain Holt to the role of commissioner, so why does he continue to antagonize and torment him? It just doesn't seem like there's any real reason for any of the successive events to happen.
Understandably, he's supposed to represent an ongoing real-world problem, which is not necessarily the corruption of the police department, but mostly the exclusionary nature of it. As Captain Raymond Holt, who is homosexual, and other competitor Olivia Crawford who happens to be a woman, are both beaten to the punch by this decrepit old man who doesn't look like he has much life left in him, never mind fight.
The storyline suffers from forcing conflict where it just doesn't exist and trying far too hard to push the message, pushing it so hard that it feels far too in your face, or even exaggerated to be taken seriously.