“Trash Fire” (*1/2 out of four) was an apt title for this horror movie trash about a young man (Adrian Grenier) and his girlfriend (Angela Trimbur) who seek refuge from their various problems by living with his bizarre grandmother (Fionnula Flanagan) who turns out to be a serious sicko who watched one too many re-runs of “Mommy Dearest.” Heavy-handed horror show is done in by well-worn story and Grenier’s weak performance. One sequence involving a snake in the toilet provides movie’s only scares.