I DRINK YOUR BLOOD (1973)
In this cult classic, a band of satanist hippies roll into town and begin terrorizing the local folk. They rape a girl, which spurs her grandfather to go after them... but he fails. The grandson steps up and exacts revenge on 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.
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