Dressing up is one of the most common things for celebrities, but from some reason on Halloween many of them get it all wrong. From the cheesy cow girl Gwen Stefani, to the obvious Kelly Osbourne and Luke Worrel (aka egg and bacon), sweeter than sweet angels Nick Cannon and Mariah Carey, messy painter Helena Christensen, over-dressed Michelle Trachtenberg and of course to top it all black crows Heidi Klum and Seal - enjoy the best of the worst celebrity costumes of 2009 Halloween.