"Two peas in an overexposed pod," Blackwell said of the skimpy attire worn by the two celebutantes he called the "Screamgirls."
Some of Blackwell's nastiest words were reserved for Camilla Parker-Bowles, a member of the British royal family, who finished No. 2 on the list.
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"The Duchess of Dowdy strikes again," wrote Blackwell. "In feathered hats that were once the rage, she resembles a petrified parakeet from the Jurassic age. A royal wreck."
Blackwell, no longer an active designer but still an acid-tongued critic of celebrity fashion, aimed his poison pen at Hollywood, with young entertainers dominating the list.
At No. 3 was actress Lindsay Lohan, scolded by Blackwell for turning "from adorable to deplorable."
Christina Aguilera was also in Blackwell's fashion hall of shame. He called her a "dazzling singer" but added that she "puts good taste through the wardrobe wringer. All crass and no class."
He referred to Mariah Carey as "Mariah the fashion pariah ... the queen of catastrophic kitsch," and "American Idol" judge Paula Abdul as "a fallen fashion idol."
He said actress Sharon Stone resembles "an over-the-hill Cruella DeVille," and Tori Spelling embodies "down and out in Beverly Hills."
"Grey's Anatomy" star Sandra Oh was faulted for too many beads and bangles. "She's layered lunacy from head to toe," Blackwell said.
Meryl Streep, who starred in the fashion-themed movie, "The Devil Wears Prada," came in at No. 10 on the annual dis-list.
"From Streep you could weep," Blackwell said. "Her beauty of a career cannot be denied, but that beast of a wardrobe is pure mother of the bride."
On a kinder note, Blackwell offered his 10 "fabulous fashion independents" — actresses Kate Winslet, Angelina Jolie and Helen Mirren, singers Barbra Streisand and Beyonce, California Rep. Nancy Pelosi, Princess Charlotte of Monaco, model Heidi Klum and actresses Katie Holmes and Marcia Cross.