Is it OK to use urban legends/urban myths in stories (without permission)? for example: candy man, bloody mary, the idea of Friday the 13th, etc.
I guess you can also call these folklore..
Also, I have the same question with fairy tales, fables and such. can anyone use those (without being sued)?
You can find lots of lists of fairy tales on wikipedia. Like
here.
In short, (in the US) you can use any of these fairy tales or urban legends in your writing. Just make sure you aren't using elements that belong to copyrighted versions of the stories. For instance: snow white is okay, the seven dwarves are okay, but Doc, Grumpy, Happy, Sleepy Sneezy, Bashful, and Dopey belong to Disney and you can't write about them.
Friday the 13th as in an unlucky day is part of folklore, and thus okay to write about. Friday the 13th as in a day that an angry mother kills a bunch of sinful fornicating camp counselors to avenge her adorable and dead son Jason Voorhees belongs to the people who made that great film, and thus NOT okay to write about.
Note: 'Candyman' isn't an urban legend as far as I know. It's a cheesy horror movie based on a Clive Barker story. So like I said, check your sources before you start writing. Have fun!