It WAS in The Exorcist. The character who said it was a movie director named Burke Dennings (played by Jack MacGowran).
Jack MacGowran as Burke Dennings in The Exorcist
Dennings is the one who the little girl, Regan, supposedly kills when she is possessed, using superhuman strength breaking his neck and throwing him out the window onto the steep staired walkway while her mother's assistant has run an errand to the store and left Dennings to watch Regan.
It's actually a gin where Dennings claims to have found a pubic hair. Here is the line from the script.
Burke Dennings: [to a prominent senator at (Regan's mother) Chris' party]. "There seems to be an alien pubic hair in my gin. Never seen it before in my life! Have you?"
This line is frequently cut from the TV versions of The Exorcist.
Shortly after this scene, Regan appears in the living room where a few remaining party guests are singing songs around an astronaut who is playing the piano. Regan announces to the piano player "You're going to die up there." and then urinates on the floor.
Anita Hill in her testimony against Thomas changed the drink from "gin" to a "Coke," but otherwise the quotation she attributed to Thomas was almost word for word from the movie.
Others who were in the office at the time she claimed he made the pubic hair query do not at all remember it. Only her, yet she claimed he made it as a general query to the office staff.
The Senate hearings even brought up The Exorcist because senators recognized the line from Hill's testimony and asked Thomas had he ever seen the movie. He testified he had not. They asked him if he had seen any scenes from the movie. He stated he had only seen the floating above the bed scene on the news.
Anita Hill claimed that Clarence Thomas referenced Long Dong Silver's performance in a porn movie in public at a party, making crude jokes about his size in comparison, and supposedly he, according to her, produced a nude picture of the porn actor. No others who were present at that party supported her story. She was the sole complainant against Thomas. From the transcript of the testimony, Sen. Orrin Hatch reported that Hill had years before made exactly the same accusation against another supervisor named "Brand" using the exact same wording about Long John Silver in county government sexual harassment case. Seems odd that the same thing would have happened to her again with the same porn star being shown to her by two different men so separated in time. . . or was this a pattern of behavior on her part?
That porn movie had nothing to do with the quotation.