Continuity mistake: When the two unlikely partners debate about ventriloquism in front of the City Hall, a woman passes behind them twice. (00:26:55)
Continuity mistake: Russell Crowe's stuntman leaps through the non-stained office window in two different ways in the scene when he's held at gunpoint by the two henchmen. (00:20:50)
Continuity mistake: The younger gangster (credited as 'Blueface' for what happens later in the scene) is sitting on his heels and asks a first time "Where is Amelia?" He stands, and in the next shot he's standing, again, and he even has both hands on the floor, which he hadn't in the first shot. (00:18:30)
Continuity mistake: A bad guy hiding in Jackson's apartment points a gun at his head when Jackson, carrying a case of Yoo-hoo, is distracted by his accomplice. In close-up the older guy takes his glasses off, but in the next wider shot he's wearing them. (00:16:25)
Continuity mistake: Holland's daughter is taking interest in Jackson's job and asks him if he can beat up her friend. Her dad quickly puts a piece of pie in front of her. His cigarette is in hand, but in the close-up of Holly he's got it in his lips. (00:26:05)
Continuity mistake: Holland is telling Jackson about the case and how his client thinks she saw her niece drive away. He punctuates this statement gesticulating with his right hand (the fit one, holding the cigarette) but in the reverse shot he's using the hand in the cast, the left. (00:24:40)
Continuity mistake: Holland is begging Jackson off after he punched him and asked him if he's a PI; his right hand is raised in close-up, floor-level in the wider angle. (00:13:05)
Continuity mistake: The writing on the cow post-it is different from the first time we see it to the time when Healy checks it out later (the most immediately noticeable difference being the length of the prime in the 'six feet' notation). (00:07:50 - 00:12:25)
Continuity mistake: When Jackson checks out the note in front of March's house, he holds it in the 'front' of the cow, but in close-up his thumb is between the cow's legs. (00:12:25)
Continuity mistake: Jackson heads out of his apartment forgetting the dusters on top of the TV. In the first shot the TV guide is open, it is closed on the close-up. (00:11:55)
Factual error: We're in the year 1977, and it's established later by multiple elements that it's October 26th. However, at the gas station March reads a headline about a killer bee in Brazil (which is a plot point, even!), which refers to real life events from November of the same year. (00:06:45)
Continuity mistake: When March nearly kills himself punching the door, the hole in the glass changes between shots; there's next to no glass left at the top of the panel he punched, then it grows back a couple inches. (00:09:50)
Continuity mistake: Jackson Healy takes the envelope from Amelia and begins counting the money. She eases the grip on the wheel in the side view, but she's again clenching it tight in the frontal view. Moreover, when he tells her she's short, she has just one hand on it; cut away a second, and she's again with the same grip as the previous part of the scene, showing two separate takes edited together. (00:07:50)
Continuity mistake: The 'big boy' goes to check the car that crashed through his house. He leans against a plain spot on the car's door, but in the next shot he does it gripping the bottom tray. (00:02:25)
Other mistake: The Nice Guys have just dropped the disfigured body onto the fancy dinner table of someone. They run away, but before the camera cuts away you can see Ryan Gosling is trying hard not to laugh. (00:47:15)
Other mistake: Misty's car at the beginning of the movie crashes into the house presumably breaking through the perimeter wall, certainly does smash through interior walls and furniture, but in the living room it still has every single light, including the side ones, completely whole and undamaged.
Character mistake: Twice over in the movie (when Healy wakes up and when March at the end of the movie drives to his place) billboards for The Comedy Store appear. The program of the evening features comedians such as Tim Allen, Richard Lewis, Robert Klein and "Elaine Boosler." So they misspelled Elayne Boosler's name. (00:10:50 - 01:48:35)
Factual error: Showing the exterior of Healy's apartment, it is established that he lives above the famous stand-up club "The Comedy Store." Showing the entrance though, they show also the board above it which is composed of signatures of famous comedians - most of them who never appeared on it in 1977, when the movie is set. For instance you can see Roseanne (Barr) 's signature on the bottom right corner, and also Pauly Shore's. (00:10:55)
