One really extreme story is a helicopter parent who moved to a different city just to be near their child's university. They would show up at the child's dorm at all hours, uninvited. Another is a parent who hired a private investigator to follow their teen when they went out with friends. And there was a case where a parent actually fought with a teacher in front of the whole class because they thought the teacher was being too hard on their child.
I know of an extreme helicopter parent horror story where a parent followed their adult child on a date. They sat at a nearby table and watched every move. It was so creepy for the child and their date. Another is when a parent called the police on their child's friends because they thought they were a bad influence, even though there was no real evidence. And there was a case where a helicopter parent actually dictated what their child should wear every day in college, as if they were still a small child. This completely stifled the child's independence and self - expression.