You can call Michael Moore (search) a lot of things — and Republicans do. They say the creator of "Fahrenheit 9-11" is a traitor, a liar, a scoundrel, but inevitably some deploy the last acceptable slur in the American arsenal of insults.

They call him ... a fat man.

Moore, who attended this week's Republican National Convention (search) as a columnist for USA Today, was greeted by delegates who derided him as a "fat pig."

Perhaps they read the book by David Hardy and Jason Clarke, "Michael Moore is a Big Fat Stupid White Man." Or they came across the suggested slogan for the Web site moorewatch.com — "Michael Moore: Putting the vast in vast left-wing conspiracy."

Or Andrea Harris' screed in her "Too Much to Dream" blog, describing Moore as "fattyfatfat, Fatty McFatperson Three-Big-Macs Corpulent Sack of Fat." Or conservative columnist Ben Shapiro's dismissal of the "fat, fraudulent filmmaker."

Now Moore is a large man. Even fellow leftist Ralph Nader (search) has said he should lose weight. "He's over 300 pounds. He's like a giant beach ball," Nader said.

But the Republicans' repeated fat insults are testimony to two truths:

1. They really, really, really dislike Moore.

2. In the 21st century, fat is still an acceptable and powerful slur.

"It is the one physical characteristic that gives people carte blanche to behave in abusive ways," says Paul Campos, a University of Colorado law professor and author of "The Obesity Myth: Why America's Obsession with Weight is Hazardous to Your Health."

The Republicans are "behaving exactly like the third-grade bullies who tormented me as a child," says Marilyn Wann, author of the book "FAT!SO?" "Any time you invoke the f-word" — and here she means "fat," not another f-word — "you're using an incredibly powerful weapon."

"They're thinking this is going to hurt him more, this is going to hurt him as a person," agrees Sandy Schaffer, New York chair of the National Association to Advance Fat Acceptance.

Moore says he once was skinny, but put on weight in the 1980s when he lived on $99 a week in unemployment and subsisted on cheap, starchy foods. He wants to lose weight, he has said.