This amazing cheapie from sexploitation director Nick Philips remains one of few examples of a rotund horror psycho (only Shirley Stoler from The Honeymoon Killers comes to mind) who, in this case, sees her enforced diet as a declaration of war in which she will take no prisoners.
We are introduced to our obese protagonist Ethel Janowski (Priscilla Alden) with images of her being restrained, drugged and straitjacketed in a mental hospital.
Her doctor lays it all out for her inquiring grandmother ("Severe paranoid manifestations, long periods of depression, violent outbursts - frankly, it's against my better judgment that she's being released."), before prescribing weekly electroshock visits and encouraging grandma to put Ethel on a diet.
The generally disinterested Ethel only comes alive when preparing a sumptuous meal of 7 eggs and a pan full of greasy bacon, commenting sardonically that, "That goddam jew doctor gave them orders not to give me enough to eat!" (This is not the film's only instance of head-shaking racist dialogue!)
When grandmother hides all the food in the house, Ethel responds by viciously stabbing her, and gives the same treatment to the grocery delivery boy (whose '70s coif is superb) when he demands $80 and Ethel only has $4.50.
When Ethel misses her electroshock appointments, the doctor comes calling and meets the same fate.
Ethel's prostitute sister Rosalie comes to stay with her for a few days, but mainly uses the house as a means of entertaining her tricks.
When her boyfriend John shows up trying to get Rosalie to take him back after a detour in Vegas with some floozie, Rosalie is reluctant because John used to slap her around.
His response is one of the film's many examples of grade-A dialogue (to match the grade-A ketchup used as blood throughout): "You need a good beating once in a while. All women do. And you especially."
When Rosalie and her greasy beau start complaining about the stench emanating from grandma's room, Ethel eschews the (logical) decision of getting rid of the corpses in favour of adding to the bodycount.
While psychedelic sequences portray the extent to which Ethel's mania has taken over, no real attempt is made to locate the source of her neurosis, although one can speculate that she is acting out against pressures to conform to traditional standards of beauty.
What gives "Criminally Insane" its lingering entertainment value is really Priscilla Alden, who performs her part with a nihilistic fuck-you attitude that's admirable in its refusal to go over-the-top, as many would be tempted to do in a role like this.
She would reprise her role 12 years later in the sequel, Crazy Fat Ethel 2 (1987).