Halloween is the best celebrity holiday: It's a chance for Hollywood A-listers to choose their own costumes, for once. Of course, some costume ideas are better than others, and while some celebrities rank as some of the best-dressed-for-Halloween stars that we've ever seen, others belong more on a Worst Dressed List than at a Halloween party.

As Halloween gets closer, now is a good time to reflect on how trick-or-treaters like Kim Kardashian, Heidi Klum and Christina Aguilera put a celebrity spin on their looks ... and to reflect on how others, like Anne Hathaway and Snooki, show us what ideas not to try for October.

We've rounded them up from worst (F) to best (A+). Click away, and Happy (Early) Halloween!