I've never been a devoted fan of David Letterman, but I've watched his show enough to appreciate his wit. He can be truly funny, and his political humor, though always one-sided, is some of his best work.

But this week he went too far.

By now, more people know about his remarks Tuesday night — about Palin, mother and daughter — than they do about the potentially regime-changing election in Iran and the stiff new U.N. sanctions against North Korea.

In his opening monologue, Letterman said that, on a recent trip to New York, Sarah Palin resembled a “slutty flight attendant” and that her teenage daughter had been “knocked up” by ballplayer Alex Rodriguez at Yankee Stadium.

Though I agree with her on some critical issues, Sarah Palin isn't my favorite Republican, and I believe she played a big role in her party's defeat in last fall's presidential election. But any person who, on national television, calls her — or any woman — a slut and suggests the same of her teenager daughter is the lowest of the low.

Deservedly, Dave is catching plenty of heat, and from all quarters. A Salon column, deriding his frat-house humor, asks why feminists are giving him a pass. Michelle Malkin accuses him of discrimination against working-class and middle-income women, in particular. Very few commentators are defending Letterman, even on the grounds of free speech.

The brand of humor that Letterman fell into Tuesday night — and I say “fell into” generously, as I suspect it reveals his normal state of mind — was despicable on all counts.

It brings to mind “Mad Men” episodes where the early-1960s advertising guys harass their female co-workers with non-stop sexual innuendo and outright verbal abuse.

It also shows just how thin is the veneer of political correctness among many who claim to speak for the progressive, hip segments of our society. If you want to see this kind of attitude in embryonic form, read through the annals of the Students for a Democratic Society and see how many of the men saw their female co-revolutionaries primarily as housekeepers and sex playmates.

We can do better, and we deserve better. It's time for Dave to go.