Paris, Fergie & Carmen Showing As Much Skin As Possible for Halloween

If you're expecting Paris Hilton, Carmen Electra, Fergie, and Dolly Parton to dress up for Halloween in something slutty ... you're smart -- but TMZ knows exactly which super-revealing outfits they picked out this year.

A rep for L.A.'s famous Trashy Lingerie store tells TMZ, all four ladies stopped in to purchase various sexy costumes.

Paris picked up 4 costumes ('cause one is so bourgeois) for a total of $3,000 -- two different fairy outfits, a sexy Robin-looking outfit, and an Alice in Wonderland costume.

1025_halloween_costumes_subDolly dropped more than 5 grand on a simple black leather pirate get up -- but it required custom tailoring for her, umm ... jack-o-lanterns. Hence the huge markup.

We're told Carmen bought a purple sequin corset with a black tutu -- and Fergie bought "mostly lingerie stuff" and a cowboy costume.

By the way ... a bunch of Hollywood costume shops told us what the most popular celeb-themed costume ideas are this year. Which one you got?