One teen girl is a fujoshi, aka a fan of "yaoi" manga (male/male romances), which in real life are often pornographic. We see a page from her favorite manga, called "Overtime Work Lovers", showing two men about to kiss (one of them might be shirtless). Her obsession with seeing gay love everywhere becomes a running gag. On multiple occasions, she walks in on the main character in weird (although completely innocent) situations with other men (once, with not one but three other men) and thinks something gay/sexual is going on.
In a brief and humorous moment, the main character ties up a seven-year-old girl to get her to stop being so rambunctious. A teen girl walks in on this and mutters, "S&M?" at which the guy is absolutely horrified and adamantly protests. In a later episode, he deliberately tries to recapture his inspiration for calligraphy by humorously reenacting this scene with his two guy friends; his mom walks in and sees this (as well as hears some very-much-out-of-context dialogue) and shrieks, "BONDAGE?"
Two teen girls briefly tease a guy in the bath and try to see him naked. (They fail.) They aren't attracted to him, though -- they're just messing around. One of the girls, who is obsessed with gay manga, brought a camera for "research" for a manga she's drawing; her friend tells her that full nudity can't be shown in manga, to which she replies (in the subtitled version) that a lot can be shown as long as you censor the "tip".
The abbreviation "S&M" is joked about in one episode, with a young girl jumping around repeating it. Will fly over the heads of young children and is all just a big misunderstanding. In the same episode, she innocently repeats some other suggestive phrases she overheard.
One character thinks two characters are kissing but in reality aren't.