I Drink Your Blood (1971)

A band of satanist hippies roll into a town and begin to terrorize the local folk. They rape a local girl and her grandfather goes after them. He fails and is given LSD. This bothers his grandson, who gets back at the hippies by feeding them meat pies infected with blood from a rabid dog. They turn into crazed lunatics and start infecting and/or killing everyone and everything in their path.