I Drink Your Blood(1970)
A band of satanist hippies roll into a town and begin terrorizing the local folk. They rape a local girl and her grandpa goes after them. He fails and is given LSD. This bothers his grandson and he gets back at the hippies by feeding them meat pies infected with blood from a rabid dog. They turn into crazed lunatics and begin killing and/or infecting everything in their path.