The Loved Ones (2009) http://www.imdb.com/title/tt1316536/
Horror / Thriller
Lola asks Brent to take her to prom. Brent declines. Lola's daddy only wants her to be happy so he helps Lola have her own prom. Meanwhile Brent went off into the field to listen to some music, but after a surprise headache he finds out the hard way he's attending Lola's prom.
There's actually a little more back story involved that shows that Brent has indirectly encountered Lola and her daddy's special relationship before, the explanation of which is doled out as the film progresses.
I think I heard about this film after reading a list about relatively unheard-of recent horror films. I've seen about half the films on the list, but the description of "The Loved Ones" seemed interesting. I've already watched a few decent films from Australia thanks to the power of Netflix and figured I'd gamble on this one. Glad I did. Granted, there weren't a lot of surprises story-wise, most events and the outcome are pretty standard horror fare, but the film was executed well.
I was pleased to see Robin McLeavy, the actress who plays Lola, again. I first saw her in "Hell on Wheels" where she plays Eva, a distinctly tattooed once-captured-by-Indians-now-turned-camp-whore character. She also played as Abraham Lincoln's mother in "Abraham Lincoln: Vampire Hunter".
Like I said, not an especially new horror-story plot, but executed well and entertaining.