GenerationofSwine
Again, like so many others I caught this on HBO when I was a kid. The difference is that this time it is NOT a bad horror movie, but an HBO original movie from back in the day when they were making some pretty stellar original movies.
"Darkly hysterical" would be the best way to describe it, especially since a lot of the humor comes from the fact that it all seems very...wholesome.
It does an excellent job of plotting a murder with a very wholesome and Leave it to beaver/Donna Reed Show feel to it and, it just works.