Before I turned 18 years old, I couldn't get into NC-17 rated movies. This seemed incredibly important to me because I, like most teenaged boys, had a slightly warped idea of what all these rating systems were about.
It turns out that my idea was only slightly warped, because it was mostly accurate. I arrived at the notion that these ratings were intended only to keep me (and other kids like me) away from the really good stuff.
After all, the movie ratings G, PG, PG-13, R, NC-17, and the almighty Unrated, were age-based. Two of them even have the target ages in their names. Other age-based restrictions included driving, drinking alcohol, voting, and paying for sex at a legal Nevada brothel. It was clear that all this fun stuff was being kept away from me just because I was "too young."
My idea about movie ratings was that they were a scale of coolness, not a scale of simple age. A movie rated "G" was likely to be incredibly boring, and aimed at kids. "PG" and "PG-13" movies could at least possibly be entertaining, but I knew there wouldn't be any decent nudity (maybe a breast flash, or a butt, but possibly only a man's butt). Certainly no simusex. Decent violence, though.
"R" was getting somewhere -- in an "R"-rated movie, you know you're going to get either a good dose of sex, nudity, violence, or swearing. All good things to a teenaged boy.
"NC-17" was that almighty panacea for every pubescent male craving -- the movie was too "dirty" even for the "R" rating, so there must be some good sex and violence in any movie with this wonderful rating. My parents hated going to see movies in theaters (with good reason -- movie theaters generally suck), but they were quite willing to let me rent any movie I wanted at a video store, and they permitted me to have my own cable box in my bedroom complete with all the wonderful premium channels like HBO and Skinimax.
This obviously immature view of how the ratings system works turned out to be incredibly accurate, and to this day I still employ a derivative of it in deciding what I might want to watch.
The original view failed to take into account one hypocritical facet of American morals -- we think sex is dirty and vile, and the more fundamental of us think violence is exactly the same. Because people like that are in the vocal minority who controls movie ratings, even the movie rating system incorporated this idea.
A movie could contain not a single bared breast or exposed genital, but be rated "NC-17" anyway because it graphically depicts intensely violent situations (like decapitation, gutting, skinning, etc.). Wouldn't want the kids to see any of that, now would we?
I finally learned, after being burned a couple times, that NC-17 wasn't a guarantee that I'd get to see nudity and sex in a movie. It meant I had to actually read the back of the box, and look for male/female pairings, hints at romance or sexual depravity, or for words like "seduction" and "irresistable" and "hot". The same applied for "unrated" movies, too. Except, with those, anytime the title included "Attraction" or "Passion" I knew I had a winner.