Most of the time when a movie's rated PG or G, parents can feel confident there's not going to be anything too adult in there. The kind of content dealt with in these sorts of movies tends to be mild and kid-friendly, and while there might be rare instances of bad language or some low-level violence, it's not usually going to be anything too bad.
There are some movies that may qualify as family-friendly, should their slightly racy jokes go over the heads of children and/or parents. However, perceptive and mature viewers may be caught out by some of the humor on offer with classic PG titles, and may well hope that any kids they watch the following with won't ask about what these jokes mean. What follows will mostly focus on older, seemingly "wholesome" classics, but with a few newer examples thrown in for good measure.
'Modern Times' (1936)
Modern Times is one of the very best movies Charlie Chaplin made throughout his career. It ended up being a swansong to his silent films and his iconic character of The Tramp, being the last (mostly) dialogue-free movie he made, and focusing on The Tramp's struggles to get by in a world constantly changing due to technological innovation.
Despite this movie being made during a time in Hollywood when movies couldn't really exceed a PG rating, it has one humorous scene that stands out as being fairly mature. One scene has The Tramp accidentally inhaling what's referred to as "nose powder," and becoming hyperactive and extra aggressive right afterward. Younger viewers might wonder what "nose powder" is, but older viewers are likely to figure out what The Tramp actually inhaled here.
'Toy Story' (1995)
For a series about toys, the Toy Story movies are surprisingly mature. The first film deals with a toy coming to terms with not being as unique as he once thought, the second unpacks existentialism and the idea of immortality, and then the third is a famously hard-hitting tearjerker for adults and children alike.
This also extends into the film's sense of humor, too, as there are more than a few suggestive, racy jokes thrown in there for the benefit of older audience members. Such jokes are likely to go over the heads of most kids, such as the moment in the first Toy Story where Mr. Potato Head has a very specific way of silently suggesting that Slinky was sucking up to Woody.
'North by Northwest' (1959)
Alfred Hitchcock was a director who had a distinct sense of humor throughout his surprisingly large filmography. Even his mostly serious movies tended to have brief moments of dark humor sprinkled throughout, so it makes sense that a comparatively lighter Hitchcock film like North by Northwest has even more humor than most.
Despite a few deaths and scenes of tension here and there, this movie about a man being mistaken for a spy and pursued across America is entertaining and funny throughout. It maintains a cheeky sense of humor right until the infamous final scene of the movie: the two main characters kiss while on a train, followed by a shot of the train passing into the tunnel, implying that what the two are about to do something that probably can't be shown on-screen.
'Beetlejuice' (1988)
One of the reasons that Beetlejuice is a great spooky movie for those who don't really like horror is that it's far more of a comedy than a horror movie. Sure, the main characters die early on, and are essentially ghosts in the afterlife for much of the movie, but it has a dark sense of humor throughout that keeps things from being too scary.
Though it might be a PG movie and filled with comedy, that doesn't guarantee the comedy is good for all ages. Betelgeuse himself has a pretty crude sense of humor, manages to say several words you don't usually hear in movies rated PG, and engages in some non-family-friendly activities throughout.
'How the Grinch Stole Christmas' (2000)
It's quite astounding how much How the Grinch Stole Christmas got away with, when it comes to rude humor. It took a relatively wholesome, classic story written by Dr. Seuss about the true meaning of Christmas and gave it what could generously be called a "post-modern spin" - in other words, it was pretty racy.
There's one scene where storks deliver babies to the citizens of Whoville, with one husband claiming the baby "looks just like" the wife's boss. There's also a scene with a "Christmas party" that involves keys being placed in a bowl, which definitely wouldn't be understood by kids. Of course, this pales in comparison to some of the humor in another Dr. Seuss adaptation (The Cat in the Hat), but it's still something.
'Alvin and the Chipmunks: The Road Chip' (2015)
The Alvin and the Chipmunks series wouldn't ordinarily appeal to grown-ups, unless they were nostalgic for the well-known characters. Still, there managed to be four live-action Alvin and the Chipmunks movies released between 2007 and 2015, with the fourth of those sneaking in a fairly risqué reference.
There's one scene where Alvin ends up sitting next to legendary filmmaker/boundary-pusher John Waters, who's made some of the most infamously disgusting movies of all time. The most notorious of these - Pink Flamingos - is even mentioned in dialogue, when Alvin mentions he's watched it. Anyone who's familiar with Pink Flamingos will probably be surprised it gets mentioned here, and might be similarly shocked that someone as young as Alvin has apparently seen it.
'Casablanca' (1942)
Casablanca might be classified as a drama/war/romance movie, but it's also surprisingly funny. Even while being set during World War Two, and focusing on themes like redemption, loss, and love, it's pretty witty throughout, with plenty of fast-paced banter to make sure the film never becomes too gloomy.
Some of the humor gets a little racy, too. Rick has a conversation with a young woman who's come to Rick's bar with her husband and Captain Renault, Rick interprets this in a dirty way, and claims Renault is "getting broad-minded." Then again, given Renault's back-and-forth with Rick often carries hints of romantic tension/flirting, maybe he's not exactly wrong to think this way.
'Ghostbusters' (1984)
It's funny to think of Ghostbusters as a film series that's popular with younger viewers. The idea of fighting ghosts is appealing to kids, sure, and the main narratives of the Ghostbusters movies aren't too adult or intense... but some of the humor can be quite racy, and more targeted at adults.
This might well be a by-product of having Bill Murray in your movie, and allowing him to cut loose with his snarky sense of humor. Elsewhere, there's quite a bit of bad language for a "kid's movie," plus some fairly adult references and scenes thrown in for good measure (the less said about the scene where Dan Aykroyd's character dreams about a female ghost, the better).
'A Hard Day's Night' (1964)
The Beatles are obviously well-regarded for their talents as musicians, but they're often overlooked for how funny they could be. Some of their lyrics are quite witty, but their sense of humor shines the most during their filmed interviews, some of the behind-the-scenes banter seen in documentaries like 2021's Get Back, and during the movies they starred in as a band.
Some of this humor could get a bit cheeky, as demonstrated in their classic 1964 film, A Hard Day's Night. There's one scene where the Fab Four get bottles of Pepsi, and John Lennon takes the opportunity to pretend to smell/snort it, likely a reference to how Pepsi's rival, Coca-Cola, sometimes gets called "Coke," and how "Coke" itself is a word with more than one meaning.
'Harry Potter and the Prisoner of Azkaban' (2004)
It's no secret that the Harry Potter movies got more mature as the series progressed. It makes sense, given that each film showed the main characters one year on from the previous film, and the (mostly) young fans of the series also got older as the actors/characters got older, meaning the films could become darker and more mature as they went on.
This didn't always translate to more mature humor, though in the case of the third film in the series, The Prisoner of Azkaban, it did, for a brief moment in the film's end credits. The Marauders Map is shown throughout the credits, which shows where people are based on the position of their feet. Given how two pairs of feet are positioned at one point, it shouldn't be difficult for older viewers to work out what these two people are doing.