The Italian mafia boss Don Corleone spoke the following line in Mario Puzo’s novel The Godfather (1969, later made into a 1972 film):
 
“He’s a businessman.  I’ll make him an offer he can’t refuse.”
 
That is, the offer must be accepted upon the threat of fatal consequences. The line became a popular lawyer joke with only a slight twist.
 
“What do you get when you cross a gangster with an attorney? An offer you can’t understand” was cited in 1989. “What do you get when you cross a lawyer with a Godfather? An offer you can’t understand” was cited in 1990.
 
   
The Godfather
By Mario Puzo
New York, NY: Putnam
1969
Pg. ? (Book 1, Chapter 1):
“He’s a businessman.  I’ll make him an offer he can’t refuse.”
 
The Internet Movie Database
The Godfather (1972)
Quotes
Don Corleone: You look terrible. I want you to eat, I want you to rest well. And a month from now this Hollywood big shot’s gonna give you what you want.
Johnny Fontane: Too late. They start shooting in a week.
Don Corleone: I’m gonna make him an offer he can’t refuse. Okay? I want you to leave it all to me. Go on, go back to the party.
 
18 January 1989, Syracuse (NY) Herald-Journal, Madison County Accent, pg. 2, col. 1 ad:
THE LIGHT TOUCH
by Gary P. Harrington
What do you get when you cross a gangster with an attorney? An offer you can’t understand.
(Gary’s Auto Parts, Inc.—ed.)
 
16 January 1990, Daily Herald (Arlington Heights, IL), “LAWYERS: Jokesters let loose with barbs,” sec. 2, pg. 2, col. 5:
What do you get when you cross a lawyer with a Godfather? An offer you can’t understand.
   
6 March 1991, The Plain Dealer (Cleveland, OH), “Open season on lawyers,” pg. 5-D, col. 4:
What do you get when you cross the Godfather with a lawyer? An offer you can’t understand.
 
Google Books
The Pragmatist
Volume 9
1991
Pg. ?:
Jon Bines
I was thinking about the Savings and Loan fiasco recently (Remember? It was before the war), and it brought to mind the old joke about what happens when you cross a Mafia don with a lawyer: You get a fellow who makes you an offer you can’t understand.
 
Google Groups: va.general
What is appropriate discussion for this group?
Greg Fife
11/23/94
(...)
Frequently Told Jokes List for alt.virginia.bashing.lawyers:
(...)
Q: What do you get when you cross the Godfather with a lawyer?
A: An offer you can’t understand
     
Google Groups: eunet.jokes
Jokes on lawyers
Gary R. Anderson
9/12/96
(...)
Q. What do you get when you send the Godfather to law school?
A. Someone who makes you an offer you can’t understand.
 
YouTube
I’m gonna make him an offer he can’t refuse
Chaîne de IsiKermesse
Uploaded on Oct 18, 2010