Arbor Day (1990)

While planting a tree as part of an Arbor Day celebration, Elmer Jacobs witnesses the horrifying slaughter of his parents by a grizzly bear. Catatonic for 20 years, he is taunted by apathetic doctors and a cruel hospital staff when he finally snaps like the branch of a tree, and begins a vengeful slaughter, reaping a crop of victims using gardening tools. Unaware of Elmer's rampage, a group of teens party in his abandoned house only to be chopped down one by one.