When celebrities are drunk, on drugs or just high on their own egos, they often engage in rants. These days many such rants are captured on cellphone videos or audio tapes and go viral on the Internet. Nothing surprising there. What is surprising to many is that the rant du jour seems to be directed against Jews.

Consider the former Dior designer, John Galliano, who was sitting in a bar in a Jewish section of Paris and announcing his love for Hitler and smiling as he told the people at an adjoining table, who he apparently assumed to be Jewish, that “People like you would be dead. Your mothers, your forefathers, would all be f – – – ing gassed.”

Or Charlie Sheen, who claims to be high on Charlie Sheen, attacking his producer by emphasizing the Jewish nature of his original name, Chaim Levine.

Or Oliver Stone telling an interviewer last year that too much attention is paid to the Holocaust because of “Jewish domination of the media.” And that Hitler wasn’t all that terrible to the Jews.

Then there is the Reverend Louis Farrakhan, ranting and raving about Satanic Jews controlling the world.

This is not an entirely new phenomenon. Mel Gibson delivered a similar rant when he was stopped by Los Angeles police in 2006. “F – – – ing Jews . . . The Jews are responsible for all the wars in the world.” Gibson then asked the deputy, “Are you a Jew?”

Generally, sobriety results in apology, but the damage has been done.

The question is: “Why the Jews?” There’s an old joke about a Nazi rally in Nuremberg where Hitler is screaming, “Who causes all of Germany’s problems?” An old man in the crowd shouts back, “The bicycle riders.” Hitler’s taken by surprise and asks, “Why the bicycle riders?” To which the old man replies, “Why the Jews?” That was the 1930s — we’re still asking the question in the 21st century.

Let me suggest two possible answers. The first is that little about the nature of prejudice has really changed, but technology has brought private prejudices into the public arena. In commenting on the Galliano outburst, Michel Gaubert, a French DJ and music designer, observed that “virulent views like those expressed by [Galliano] are not rare.” But “the public expression” of intolerance is unusual and particularly troubling, according to patrons of the bar in which Galliano expressed his bigoted views. The pervasiveness of cellphone videos and the widespread use of the social media have blurred the line between private and public expression. What used to be only whispered to friends at a bar is now broadcast around the world.

There is a second, a far more troubling answer to “Why the Jews?” Prominent public figures have blurred another line as well — the line between anti-Zionism and anti-Semitism, between attacking the Jewish state and attacking the Jewish people.

Consider widely publicized remarks made by Bishop Desmond Tutu, winner of the Nobel Peace Prize and the American Medal of Freedom, and a man openly admired and praised by President Obama. He has called the Jews “a peculiar people” and has accused “the Jews” of causing many of the world’s problems. He has railed against “the Jewish Lobby,” comparing its power to that of Hitler and Stalin.

He has said that “the Jews thought they had a monopoly of God: Jesus was angry that they could shut out other human beings.” He has said that Jews have been “fighting against” and being “opposed to” his God. He has “compared the features of the ancient Holy Temple in Jerusalem to the features of the apartheid system in South Africa.” He has complained that “the Jewish people with their traditions, religion and long history of persecution sometimes appear to have caused a refugee problem among others.” Tutu has minimized the suffering of those murdered in the Holocaust by asserting that “the gas chambers” made for “a neater death” than did apartheid. He has demanded that its victims must “forgive the Nazis for the Holocaust,” while refusing to forgive the “Jewish people” for “persecute[ing] others.”

He has has accused Jews — not Israelis — of exhibiting “an arrogance — the arrogance of power because Jews are a powerful lobby in this land and all kinds of people woo their support.”

Tutu has acknowledged having been frequently accused of being anti-Semitic, to which he has offered two responses: “Tough luck” and “my dentist’s name is Dr. Cohen.”

Former President Jimmy Carter too has contributed to this new legitimization of Jew-bashing, by echoing Tutu’s derisive talk about the Jewish domination of America (“powerful political, economic and religious forces . . . that dominate our media”) and his use of the term “apartheid” in his book about Israel.

By thus blurring the line between legitimate political criticism and illegitimate bigotry, widely admired people like Tutu and Carter legitimize the kind of anti-Semitic attitudes that manifest themselves in the rants of celebrities like Galliano, Sheen and Gibson.

This blurring has also affected the tone on university campuses around the world, where Tutu and Carter are particularly admired and imitated. I speak at universities and had never, until recently, heard and seen the kind of language now being directed against Jewish students and faculty who support Israel.

So I was not as surprised as some by the recent celebrity rants. The oldest prejudice has never quite disappeared. It just went underground — waiting for the right moment to fester.

Alan Dershowitz’s latest novel is “The Trials of Zion.”