Green Book's Made-Up Scene

The movie Green Book is "inspired by a true story" about an Italian American bouncer who takes a job driving a black pianist (Don Shirley) on a tour through the Deep South in 1962. But as always it doesn't stick closely to the facts. In one scene, Tony "Lip" Vallelonga punches a cop who accuses Italians of being part black:

PATROLMAN #1
What's this last name say?

LIP
Vallelonga.

PATROLMAN #1
'Hell kind of name is that?

LIP
Italian.

PATROLMAN #1
Oh, now I get it. That's why you driving this boy around... you half a nigger yourself.

Since that sounds more like something that would be in a dumb Spike Lee or Quentin Tarantino movie, or posted online by some Afrocentrist or Nordicist troll, I decided to check if it really happened. That scene is actually based on two separate events:

There were a lot more things that happened with the cops, and we combined two, when my father punched out a cop and that was one time they got arrested. They also got arrested when they were going 25 mph and a cop said they were doing 75. It was a shakedown and the cops were pissed my father was driving this black man.

The one where the cop is mad about a white man driving a black man around was only about that and had no violence and no mention of any name-calling:

Tony and the Mississippi policeman argue about the fact that Tony is driving a black man. The policeman calls Tony a racial slur, and Tony punches him. The camera pans to the two men in a jail cell. [...] In Shirley's own telling, Tony didn't throw blows, Shirley was not arrested, and they were driving through West Virginia.

"What happened was they stopped us and charged us for speeding in a 35 mile (per hour) zone we were going 25, okay, but they said we were going 75, and it was all pure racism," Shirley said in an interview with Astor. "They got pissed because he was white, driving me. That's what it was about. They made us turn around and come back 50 miles to McMechen, West Virginia, okay?"

The one where Tony punches the cop happened later and it was because he was called an ethnic slur for Italians, not blacks:

Did Tony Lip and Don Shirley really end up in jail due to Lip punching a police officer?

Yes. Lip became enraged at the officer for calling him a derogatory name for Italians. Lip did punch the officer and they ended up in jail, but it happened a year later, in the fall of 1963.

So there's no evidence that any cop ever made that claim. It was very likely invented by the writers and put in the movie to make a point about racism and "whiteness":

The point of the film is, to a certain extent, that because Tony is experiencing these prejudicial encounters with Don, that they slowly chip away at his conditioned hostility and he begins to view people of colour as something approaching equal. At one point, a police officer pulls over their car and seems intent on humiliating both Tony and Don, and calls Tony 'half a nigger.' To which Tony responds in the only way he knows with a swift one to the jaw. This is presented as pivotal by Farrelly, a Damascus moment where Tony experiences life as a member of the oppressed. But in actuality, Farrelly is showcasing a kind of inverse Uplift Suasion, where instead of a high achieving person of colour changing a racist mind via the sheer will of their achievement, a white person literally has to be called a 'nigger' before they begin to contemplate racial equality.