Just like some of the wackier Aronofsky films, the plot doesn’t make much sense, but that’s OK, it’s more about the visuals, and oh boy does it deliver.
Annoying brat starts nagging his driving parent, so they get into an accident. She survives, but gets implanted with a titanium plate in her head. Years later, still living with her parents, she is nearly raped at a car show she was at (doing exotic dances on a Cadillac), and gets impregnated by said Caddilac.
After a couple more murders for no reason, she settles in with a older man, pretending to be his long disappeared son. He “falls” for it, just wants to be with someone. Some friction with his existing relationship ensues, but our protagonist dodges several metaphorical bullets. The final reveal comes nearly at the end, but her new “father” doesn’t care, she is like a son to him. He assists her in giving birth to the human-car hybrid and dies in a pool or motor oil.
The protagonist is as unsympathetic as it can be, it goes all in into the cruel murders. All for nothing.