Reputed Boston mobster James “Whitey” Bulger was reprimanded by the judge overseeing his racketeering trial Thursday after Bulger reportedly called a government witness a “f----- liar” during his testimony.

U.S. District Court Judge Denise Casper did not hear Bulger cursing, but she scolded the former reputed Winter Hill Gang leader after Assistant U.S. Attorney Brian Kelly alerted her to Bulger’s potty mouth.

Kelly said Bulger, who spent more than 12 years on the lam before being arrested in California in 2011, “spent his entire life trying to intimidate people.”

But “he should not be doing that in federal court,” the prosecutor said, according to the Associated Press.

“I know he spent his whole life trying to intimidate people in South Boston, including 15-year-old boys,” Kelly added, according to the Boston Herald.

Bulger’s cursing was directed at government witness and rogue FBI agent John Morris, who testified that Bulger was an informant for the bureau.

While Morris was on the witness stand, Bulger called him “a f----- liar.”

Prosecutors contend ex-FBI agents helped Bulger evade authorities for years. They claimed Bulger was an FBI informant who passed along information about Italian organized crime in exchange for the FBI not looking into his crimes. Bulger’s story was the inspiration for the 2006 Oscar-winning film “The Departed.”

Bulger’s cursing during Thursday’s testimony wasn’t the first time he's used vulgar words in open court.

When prosecutors mentioned Bulger being an informant during their opening statement, Bulger uttered, “I’m no f------ informant,” according to the New York Daily News. Bulger reportedly cursed under his breath and was heard by someone within earshot of the defendant.

Bulger has been accused of orchestrating or participating in 19 murders in the Boston area in the 1970s and 1980s. He’s also been charged with a number of racketeering crimes, including extortion, weapons charges and money laundering. Bulger pleaded guilty to the charges.

Bulger was indicted in 1994 and spent 12 years on the FBI’s Ten Most Wanted Fugitives list before being captured in June 2011 in Santa Monica, Calif.