Trick 'r Treat (2008)

AKA: Trick or Treat
Director: Michael Dougherty
Genre: Comedy | Drama | Horror | Thriller
Runtime: USA:82 min
Country: Canada | USA
Language: English
Starring: Anna Paquin, Brian Cox, Dylan Baker, Tahmoh Penikett

Plot: Four interwoven stories that occur on Halloween: An everyday high school principal has a secret life as a serial killer; a college virgin might have just met the one guy for her; a group of teenagers pull a mean prank; a woman who loathes the night has to contend with her holiday-obsessed husband.

http://www.imdb.com/title/tt0862856
http://en.wikipedia.org/wiki/Trick_'r_Treat