It's an outrageous, vulgar comedy about sixth-graders (11-12 years old and they look younger) and it flopped in Japan. Its second season was cancelled halfway through. It's more popular in the West, though.
It's also very funny. It's appalling, yes, and you'll often be cringing. Boobs, underwear, blood, urine, humiliation and more are thrown around, sometimes literally. The show's central joke is that the children have only a rudimentary understanding of what they're talking about, so they won't actually realise when their conversations and more turn into a nuclear blast of innuendo. Sometimes they'll be saying it in all innocence. Sometimes they're trying to brag and pretend they're more grown-up than they are. Two of them are sleazebags, but in a slightly clueless way that doesn't add up to anything. Sometimes they're evil-minded little monsters who trying to get their "friends" in trouble, or else are just being weird.
Oh, and characters quite often smack into something (usually the ground) and generate a pool of blood. This is always funny.
Some of the show's best sequences are the ones where the children have simply decided to do something bizarre, e.g. the "ice bowling" in I-9 or the "curling with humans" in II-7. There's a dialogue-free musical sub-episode. There's ludicrous, mind-boggling escalation (all the time) and Futaba eating a hat. The children's teacher, Yabecchi, brings his unnamed pet hamster into class and the children name it "Nipples". Everyone loves Nipples and plays with her, but unfortunately one day Nipples gets stressed and Hitoha-chan declares that she's going to be the only person allowed to look after the hamster...
"I want to pet Nipples for real!"
"Yeah, I want to see Nipples every day!"
"Poor Nipples hasn't been feeling well."
"Everyone crowds around, pinching and squeezing, until she's too sensitive to take it. You're all too rough with my Nipples!"
"What do you mean, 'your' Nipples? She belongs to the whole class!"
"I was gentle, I swear!"
"I want to see Nipples grow up and get bigger!"
"But when you stroke Nipples slowly and gently, you can tell she just loves it!"
"What if everyone got a turn to take care of Nipples, Yabecchi?"
"Good idea. Hitoha-chan, maybe you should have a little more faith in everyone else."
"Give me a chance to handle your Nipples!"
"We'll all take good care of your Nipples!"
"Nipples! Nipples! Nipples! Nipples! Nipples! Nipples! Nipples! Nipples! Nipples! Nipples! Nipples! Nipples!"
"Everyone loves Nipples just as much as you, Hitoha-chan. Including me!"
"Awake! Standing up!"
"Nipples is standing straight up!"
"It's okay for me to touch your Nipples, right?"
"Yes, go ahead."
The scene's less filthy in English translation, incidentally, due to pronouns and prepositions. Despite being all in innocence. Most of those lines are from girls. If you muted the sound, you'd think it was a heartwarming scene. Naturally, there's someone listening at the door... and that's just ep.1. That's a warm-up. The show's just getting started.
The show's core troublemakers are non-identical triplets, Mitsuba, Futaba and Hitoha.
1. Mitsuba has a horrible personality, puts her friends down and sadistically enjoys other people's pain and humiliation. She's also the most normal of the three (underneath) and is a golden target for gross, childish or depraved humiliation that she usually brings on her own head. In the show's second half, she develops a bit of a weight problem. (It might be inherited. Their father is huge, unshaven and supposedly looks so suspicious that the police keep dragging him away. Personally, I don't see what's so dodgy-looking about him, but hey.)
2. Futaba is the only triplet with social skills. She's lovable and gets on wonderfully with everyone, with the boys treating her as male because she's obsessed with porn and boobs. However she's also got superhuman strength and a flea's attention span, so she's liable to destroy furniture and/or become non-sentient if she's got a bit too carried away with playing.
3. Hitoha is rude, scary-looking and uninterested in other people. She'll read a book while you're trying to talk to her, or perhaps hide under your desk. Underneath, though, she's capable of odd enthusiasms (animals, superhero TV shows) and of getting frustrated at her problems with social interaction.
Is it in good taste? Ahahahahaha, no. It is, though, surprisingly harmless. It never goes within a million miles of actual sex, despite crossing other kinds of deeply inappropriate lines. The adults are all good, well-meaning teachers and guardians who'd sooner die than do anything bad. Also, crucially, the show itself isn't sexualised. It's not aimed at perverts. The art's cartoonish and people's heads are spherical.
It's funny and inventive, but it's also basically a bunch of outrageous gags and I don't imagine I'll ever see the need to rewatch it. Season 2 isn't as good as Season 1. At its best, though, it achieves gutter brilliance.