Depending on the town's inhabitants, you can also have villagers commenting that other villagers of the same gender should hook up.
In City Folk, you can harvest mushrooms during the fall. Some of them resemble psilocybin containing mushrooms. The furniture you get from these also resembles various psilocybin containing mushrooms. Your character can actually eat the mushrooms that do not contain furniture.
The character Pascal. His mannerisms (and speech), seem vaguely like what you'd expect from someone using some kind of drug. (However, sometimes villagers will tell you that he was perfectly normal before an accident from playing sports occurred.)
In the GCN version, Tom Nook's greeting upon entering his store includes the line "Feel free to browse, but try not to carouse!" To carouse is to drink lots of alcohol and party heartily.
When you capture a stag beetle, the protagonist makes a pun about stag parties, another term for bachelor parties.
In the German version, one of Mr. Resetti's rants conclude with him going to watch "Der Bewegte Maulwurf" (The Moved Mole), a play on Der bewegte Mann (The Moved Man), a famous German movie—based on a comic—about a straight man being thrust into homosexual subculture.
In some of the games you can obtain a statue of a naked mermaid, as well as the Manekkin Pis (statue of a peeing boy) and the Venus de Milo (statue of the Roman goddess of beauty, which happens to be topless). The stark-naked Michaelangelo's David joins them in New Leaf.
Wild World makes reference to alcohol in the fly's bug menu description.
In New Leaf, you can crossdress. That doesn't necessarily fall into this trope, but what Mabel says when a male tries on a dress at the store DOES.
Mabel: Well, I guess it's okay to be adventurous sometimes.
Again in New Leaf, there's a Double Entendre storm when a cherry salmon is caught: it mentions "cherry salmon pie".
Big Sister villagers may mention turf wars in other towns before they move there. They then mention that it's because slinging turf around sounds like fun.
The grumpy villagers in the GCN game would sometimes mention that "(They're) built for comfort and not for speed."
Upon donating the final piece of the plesiosaur fossil set in Wild World, Blathers will say:
The plesiosaur was discovered just 35 years by high school students. I shan't tell you what my greatest high school accomplishment was...but thanks for the donation!
In one of Kapp'ns songs, he sings about getting married and singing love songs to his wife. Then he sings: "I gots ta be careful what I sings about now. As a Dad there's some stuff I can't allow."
There is a magazine with the picture of a female mole in a yellow bikini on the cover lying around Resetti's headquarters. She has a little heart next to her making it even more obvious it's an adult magazine.
In Wild World, one conversation between a Normal villager and a Lazy villager results in the Normal villager accusing the Lazy villager of being sexist. How much child-friendly media can you think of where the word "sexist" is used?
Sometimes when getting a fortune in New Leaf, Katrina will precede the fortune with the following bit of Too Much Information on Reese and Cyrus:
Pink and blue alpacas...
Oh my, what's this?...
Still on their honeymoon, I see...
In New Leaf, on Halloween, the villagers in town will sometimes ask you questions. If you mess up on a question that a grumpy villager has asked you, this is how they sarcastically:
In New Leaf, Kapp'n is not allowed on the island, because Leilani is sick to death of his singing. This is basically the equivalent of a lovers spat in which the husband is kicked out of the house until further notice. (In a cutesy kid-friendly Nintendo game)