It's a pure gag manga filled to the brim with toilet humor and puberty jokes. The theme is generally about stuff like hair, nudity, sex, toilets and similar things.
Sure, that sounds really childish, but it's actually quite hilarious as long as you don't expect more than a good laugh from a manga that was never meant to be taken seriously. It's over the top with a lot of "forced" jokes, which means that these things really wouldn't happen in reality. In this particular circumstance, I feel like that doesn't take away from the comedy because it was never supposed to be anything else than a fun manga set in a wacky manga universe. Things here are just impossible, it's pretty much about normal issues tuned up by hundreds of times until you reach something surreal. You can relate to the things in this manga even though it's overdone on purpose.
I tried to write some explanations about the situations in this manga, but after trying for a while, I realize that it's a very hard manga to describe. The jokes are quite absurd and they don't work at all without the cast and pictures. When I try to actually describe the funny parts, it turns boring and would probably make people averse to try it rather than give it a shot.
However, let me get this straight, if you love absurd/nonsense comedies whose only purpose is nothing but delivering one low-brow joke after another, you're absolutely going to love this manga. There's no story or anything serious here, it's just a machine gun barrage of ridiculous jokes. Give it a try, even the first one or two chapters will give you a very good idea about how the rest of the manga will play out and they're only several pages long.