The Slumber Party Massacre (1982) 
I didn't really like this at all. It's one of those 'nothing happens for an hour then everything happens in the last 20 minutes' film. But like that first hour was so boring, and the last 20 minutes was slightly less boring!
Disappointing, this one had been on my radar for a long time. Oh well you can't win them all!
(what's with all the 4 & 5 star reviews on Letterboxd, did we watch the same film?)