Testifying under oath in the staid halls of U.S. District Court in downtown Los Angeles, Hustler publisher Larry Flynt opined on where the next generation was taking the adult entertainment industry.

“I think there’s a thin line. As a society we’ve come to accept what I like to refer to as ‘vanilla sex,’ ” he said. “But if you get too trashy, people get uncomfortable.”

Flynt took the stand Tuesday in the first day of his federal trademark infringement trial against his nephews, Jimmy Jr. and Dustin, who earlier this year launched their own line of adult films under the name “Flynt.” Calling their films “inferior products” and “knock-off goods,” the porn mogul promptly sued, accusing them of trying to ride on the coattails of his fame and muddying the quality his customers have come to expect from his products.

The younger Flynts contend that they have a right to do business under their own name and that their uncle is just trying to stomp out competition. They say they’ve built up their own name in the industry over the years by working for the Hustler empire.

The trial, expected to last about a week, promises to be filled with many images of ample-chested women and serious argument over the inner workings of the pornography industry.

Daniel DeCarlo, an attorney for Flynt’s nephews, told the four-man, four-woman federal jury that consumers of porn are “careful and discerning” when it comes to choosing products. Because they are well-versed with the brands that are out there, and carefully study the box before making a purchase, there is little chance that the nephews’ line will be confused with Larry Flynt’s films, he said in his opening statement.

Larry Flynt’s attorney, on the other hand, said that a survey by his expert found that consumers presented with images of the nephews’ films -- with the Flynt name displayed across the top in silver block letters -- overwhelmingly associated the product with Larry Flynt.

The nephews’ effort to take advantage of their uncle’s fame was clear in one of their promotional fliers, which advertised, “You know the name, you know the game,” attorney Mark Hoffman argued.

The 67-year-old Flynt, wearing a green tie and seated in his gold-plated, velvet-lined wheelchair, testified that the feud began after he fired his nephews in late 2007 for being unproductive after keeping them under his wing for more than 10 years.

“This was a very painful thing for me to do. I didn’t wish them bad at all,” he said.

He testified that he found out through an industry publication that his nephews were using the severance money he paid them -- $100,000 each -- to launch a competitive line under their family name.

He said their films -- which include titles such as “Positive Exposure” and “Sex at Your Service” -- did not live up to his standards.

DeCarlo, the nephews’ attorney, took issue with Flynt’s assessment of the films as “trashy.” He proceeded to show the jury an enlarged image of one of Larry Flynt’s films, “Mason’s Sluts.”

“Is this less trashy or more trashy than my client’s product?” DeCarlo asked.

“Your clients are focusing on the boob element, so to speak,” Larry Flynt replied. “I just think that’s sort of passé, and guys are moving past that. That’s only my opinion.”

Dustin Flynt, said it was difficult for him to go up against his uncle in court because he had a close relationship with him, having worked as his personal assistant for many years. But his films, he said, were anything but trashy.

“We’re bringing elegance back to erotica,” he said.

victoria.kim@latimes.com