BrainGilmore posted his list, so I purposely tried to not use any of his picks.
You don't get much worst than serial killer Gerald "Jerry" Blake in the "Stepfather". What worst could a father do than attempt to murder you, "The Shining" style? see more on The Stepfather
Michael Brody has been haunted by sharks, in Jaws, he was put in the hospital by one. In Jaws 3-D, he won't go into the water. Then Jaws the Revenge came out (and pretended that Jaws 3-D didn't exist... it also pretended to be something that should be taken seriously). Brody's younger brother is killed by a shark. So he gets his mother to move with him and his kids to the Bahamas. You know, get away from the water. It's here that he finds a great white shark, Michael knows the dangers of this shark, but he keeps it a secret so he can "study" it. HIs daughter is almost eaten by the shark a few days later.
Also Rankedsee more on Michael Brody
Duane Bradley's Father
Now to be fair, Mr. Bradley's son Duane had a strange birth defect, he was born with a face and arms attached to the side of his body that was still very much alive and breathing. Duane and his half brother loved each other very much but their father couldn't bear to be the "father of a freak," so he had them separated and had the "mutation," which was still technically his son, thrown into the trash. No wonder the brothers got revenge by sawing him in half.
Harmony Lane's father in Shane Black's Directoral Debut film "Kiss Kiss Bang Bang" seems like a harmless old man, and he probably is at this point in the film. But that doesn't stop Val Kilmer from beating the s**t out of him for being sexually abusive to his daughters and being the main reason for his youngest daughter's death