Celebrity Halloween Costume Roundup, Including Kim Kardashian, Ryan Seacrest . . . and Avril Lavigne's Ex-Husband Dressing as Avril?

Xtina was a sloppy ???? I don't have a clue.

With Halloween in the middle of the week, you get TWO weekends of Halloween costumes. Here are some of the costumes celebrities wore out this weekend . . .

In a VERY strange decision, Deryck Whibley from Sum 41 dressed as Avril Lavigne. That's his EX-WIFE. And Deryck's new girlfriend, Ari Cooper, dressed as Chad Kroeger from Nickelback . . . who's Avril's new husband. I'm . . . confused.

Emma Roberts dressed as her aunt, Julia Roberts, from "Pretty Woman". Emma is 22 ...

Julia was 24 during "Pretty Woman".

Kim Kardashian ended up dressing as a mermaid. She wore a blonde wig, shell bra top, and long green skirt. Kanye West either dressed as a generic sailor or he didn't dress up and just thinks the nautical look is in style.

Hilary Duff dressed in a Dia de los Muertos-style skeleton costume.

Ryan Seacrest and Julianne Hough went for Bonnie and Clyde costumes.

Seal dressed as Kevin Garnett from the Boston Celtics . . . in that he wore Garnett's jersey and Celtics warm-up pants and, like Kevin, he's black and has a shaved head. He was also with a random woman in a Kobe Bryant jersey.

Puff Daddy dressed up as Prince.

Paris Hilton went for a "sexy 'Alice in Wonderland'" costume. Her boyfriend, River Viiperi, mostly dressed as the Mad Hatter from "Alice in Wonderland". We say "mostly" because he wore the hat and coat and vest . . . but also jeans.

Josh Duhamel and Fergie dressed as Dennis Woodruff and Angelyne. You're probably a happier person if you don't know who they are. They're two people who are legendary in Hollywood for their lifelong efforts to break into show business.

Jessica Alba, her husband Cash Warren, and their daughter dressed as the cast of "The Incredibles".

Liam Payne from One Direction dressed up in what looks like a VERY expensive Batman costume.