"In barely there bombs, she's a taste-free pain. Let's crown her the Tacky Temptress of Wisteria Lane," he wrote in a statement released Tuesday.
Lindsay Lohan was the next target of the acid-tongued critic, who called the starlet "over-hyped and under-dressed."
Blackwell gave kudos, however, to "fabulous fashion independents" Nicole Kidman, Natalie Portman, Barbara Walters, Kate Winslet, Annette Bening, Oprah Winfrey, Scarlett Johansson, Gwen Stefani, Jennifer Garner and Sheridan's on-screen nemesis Teri Hatcher.
This is the 45th year that Blackwell, a former fashion designer, has offered his best- and worst-dressed list.
Last year's worst-dressed star, hotel heiress Paris Hilton of "The Simple Life," dropped to No. 5. "This is one Hilton that should be closed for renovation!" according to Blackwell.
Other fashion losers include Anna Nicole Smith, Meryl Streep, Paula Abdul, Britney Spears, Courtney Love and Serena Williams — whom Blackwell described as "courting disaster."
Sisters Jessica and Ashlee Simpson tied for third place. "These two prove that bad taste is positively genetic!" Blackwell said.
Blackwell said he couldn't wait to bid farewell to 2004, the year of many "wardrobe malfunctions."
He added: "Here's hoping 2005 takes the ultra-feminine look to new heights. Elegance, classicism and restraint are never out of style. Neither is a good 3-way mirror."