I Drink Your Blood - David E. Durston - USA - (1970)

http://www.imdb.com/title/tt0067229/ 

Plot from Imdb: "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."

Exploitation to the max ! I think this mixes up almost every genre in the exploitation sub-genre: Hicksploitation, Sexploitation, Zombiesploitation, Hippiesploitation, Drugsploitation, Cannibalsploitation and others "sploitation"... As many 70's exploitation movies, it has some realism in it, the group of fucked up crazy hippies seems very "possible" (think Manson) and the clash with the hillbillies from the small town even more likely. Nicely paced, the murder rampage doesn't take too long to unfold and it's really funny. Well, if you find cutting heads with a machete funny. Guess I do.
Enjoy this all time classic of gory cinema, following in the footsteps of Herschell Gordon Lewis.

Trailer: