When Howard Stern's movie, Private Parts, was in the theater DH and I went to see it. A few minutes before the lights went down a lady and 3 or 4 kids, aged probably 8ish to young teen, walked in and found seats near the front. DH and I exchanged looks. About 15 minutes in they got up and left. Someone yelled "What the hell did you think you were going to see, lady?"
Perhaps she was an innocent and unworldly soul, unfamiliar with certain commonly-used expressions; and had thought that the film was going to be a comic / patriotic romp for kids, with an army setting (language suitably cleaned up) -- "the son of Mrs. Parts, joins up" ??
I'm betting that the young teen had heard from older teens that this was a really funny and cool movie, and had convinced Mom to take them...without quite realizing how inappropriate it would be for younger siblings. Surely no one is stupid enough to ask their mother to take them to that movie, knowing how raunchy Howard Stern can be!
But really, what was your first clue? That it was R rated? Under what circumstances can a person believe that an R rated movie would be OK for an 8 year old? Although the mother of my Little Sister once urged me to take her to the movies even though I thought there was nothing appropriate playing, saying that 'JFK' would be OK, since it was history. I don't remember JFK's assassination, but I've heard stories from slightly older kids about how traumatic it was for them to hear about; there was no way I was taking a 10 year old to the movie. She was old enough to be traumatized by it...and if she wasn't upset by it, I sure didn't want that information. It's entirely too easy to connect with the grief of the First Family in those images, and if you can't, then part of your moral compass is missing.