At a certain point, I'm not quite sure when, Halloween started becoming more about adults and their desire to dress up than kids. While I was always aware that Halloween had started skewing older, it was when I briefly worked for a large Halloween retailer back around 2000 that I really started noticing.
While we had plenty of costumes for the tykes, our section of adult costumes – especially sexy costumes for the ladies – was ever-expanding. Not far from the role-playing costumes you'd find at any decent adult retailer, women don't have to settle for the old standby costumes like Witch or Cat anymore. If you can put the word "Sexy" in front of it, somebody will sell it to you. Though they make no guarantees you'll look anything like their models.
With that in mind, I suppose it's no surprise that you can find long lists of Halloween-themed porn movies, including the hysterically-titled THAT BITCH ATE OUR WITCH and RE-PENETRATOR, the porn version of my all-time favorite movie (one reviewer claims it's "much better than XXXORCIST", so that's good to know).
Last but not least you can even head over to Adam & Eve's website and vote in the Halloween Sex Toy Costume Contest. No, it's not people dressed up as their favorite sex toys, but sex toys donning costumes and posing as such pop culture icons as KISS, Pac-Man and HELLRAISER's Pinhead, not to mention childhood cartoon faves Gumby & Pokey.