Certain types of sleep training. Specifically, letting a newborn baby "cry it out" in another room, till the child has screamed for an hour and often vomits, until it finally falls asleep.

A horrible, horrible practice, largely confined to the US I might add. Some pediatrician wrote a book advocating it, and now there are all these parents convinced that it's ok.

I actually had a woman (a real estate agent) push one of these books on me. As soon as she left, I threw the book in the trash and washed my hands.

Pediatricians in the US seem to like advocate child rearing practices that are "based on science" but in reality, unnatural and insane.