When a 45-year-old grandmother doesn't take kindly to jokes about a pregnant daughter, a murder victim is dismissed as a mass murderer, and the nation's first Latina nominee to the Supreme Court is herself deemed a racist, it's time for the Muzzle Meter.

Recall that the Muzzle Meter (MM) is my measuring rod for evaluating speech with possible PC implications. A high score indicates truly offensive speech (like Mel Gibson's anti-Semitic drinking binge - a 10 on the MM), while a low score means the outrage is unwarranted (as when then-Sen. Joe Biden called Barack Obama an "articulate and bright and clean and a nice-looking guy" - a zero on the MM and a comment Obama obviously forgave).

It's all gut-based. No science here and no political litmus applied. Like Supreme Court Justice Potter Stewart once wrote about pornography: "I know it when I see it. . . ."

Sarah Palin and David Letterman. The saga began after the Palins spent a weekend in New York. Soon afterward, Letterman dedicated part of his opening monologue and his entire Top 10 List to the Alaskan first family's visit.

At the show's outset, he noted "one awkward moment" from Palin's attendance of a Yankees game: "During the seventh inning, her daughter was knocked up by Alex Rodriguez." The problem? Willow Palin, 14, had accompanied her mom to the game.

Then came the Top 10 List, which featured purported highlights of the Palins' weekend in the Big Apple. No. 2: "Bought makeup at Bloomingdale's to update her slutty flight attendant look."

This calls for a multitiered scoring. With regard to the "slutty flight attendant" joke, Palin is a national public figure who was subject to this ridicule on a late-night comedy show. She should be able to handle such irreverence as it comes with the celebrity profile she herself has cultivated. MM Reading: 2.

Worse was the joke about impregnating her daughter. Letterman insisted that he was referring to Bristol Palin, who's 18 and already a mother. But as delivered (he didn't specifically mention either daughter by name), the "knocked up" joke garners an MM Reading of 8. If Letterman had made clear he was referring to the 18-year-old, that score could be halved, but it was the 14-year-old at the game.

Most insightful has been the reportage of the Washington Post's Paul Farhi, who tabulated the number of times late-night comedians made light of the Palin pregnancy last fall during the campaign. Some jokes were in worse taste than Letterman's, which raises the question: Why did this one draw such a reaction? Letterman's timing was waaaay off.

(Am I the only one wondering what A-Rod thinks?)

Leon Panetta. The CIA director, discussing Dick Cheney's frequent public criticism of the Obama administration's approach to the war on terror, told the New Yorker that "it's almost as if" the former vice president was "wishing that this country would be attacked again, in order to make his point." John McCain called that comment "really out of bounds," and the former VP said he hoped "his old friend Leon" was misquoted. Then, a CIA spokesman sought to defuse the controversy by saying Panetta was "simply expressing his profound disagreement with the assertion that President Obama's security policies have made our country less safe."

The "clarification" by the CIA was warranted. Political opponents can disagree over the tactics employed to prevent terror, but it crosses the line to say a public servant wishes for such a result. MM Reading: 7.

Randall Terry. The founder of the antiabortion group Operation Rescue said George Tiller, the abortion doctor shot and killed at his church several weeks ago, was "a mass murderer and, horrifically, he reaped what he sowed."

Whatever Tiller did while alive, he did within the bounds of the law. The same cannot be said for the man who gunned down Tiller. Terry offered an unwarranted legal (and moral) equivalency between Tiller and Scott Roeder, the man charged with the murder. MM Reading: 9.

Rush Limbaugh and Newt Gingrich. "Obama is the greatest living example of a reverse racist, and now he's appointed one . . . to the U.S. Supreme Court," El Rushbo pronounced on his show after the president offered Judge Sonia Sotomayor as his nominee for the high court.

Meanwhile, Gingrich, the former speaker playing footsy with a run for president in 2012, tweeted his displeasure: "White man racist nominee would be forced to withdraw. Latina woman racist should also withdraw." (He has since admitted, "The word racist should not have been applied to Judge Sotomayor as a person.")

No doubt both had Sotomayor's 2001 speech, "A Latina Judge's Voice," on their minds when they invoked the r-word. That's the now-infamous address during which Sotomayor said she would hope that a wise Latina judge "would more often than not reach a better conclusion" than a wise white male.

Gingrich was correct in his retraction. Criticism of the 2001 speech is, of course, within bounds. Labeling her a racist is not only wrong and appalling, but it also demeans real discourse as to her fitness to serve on the court. MM Reading: 8.

Michael Smerconish's column appears Thursdays in the Daily News and Sundays in Currents. He can be heard from 5 to 9 a.m. weekdays on "The Big Talker," WPHT-AM (1210). Contact him via www.smerconish.com.