“My Sister’s Serial Killer Boyfriend” (*1/2 out of four) was disposable trifle about a young woman (Revell Carpenter) who starts taking self-defense classes and falls for her Mr. Charming instructor (Rib Hillis) but her sister (Brianna Cohen) soon investigates and begins to suspect there may be more to him underneath his exterior. Laughably obvious and predictable and lauded with plot holes. Anyone who has seen a thriller before will be miles ahead of this clinker.