Adaptation Displacement: The anime is vastly more remembered than the manga, which is a shame as the manga is the better work. There were also two live action films with a rather surprisingly famous cast.
Fridge Horror: The students rarely get punished for groping, flipping skirts, and undressing women (it's not always Machiko). What will these boys turn into when they get older?
Worse still when you realize that one of the major complaints about the show were that students were emulating the kids in real life.
Fridge Logic: You would think she would stop wearing skirts after the twentieth time they are flicked up.
Not only that, but if she has to stand up in front of a crowd (school play, PTA meeting, fashion show, etc.), Kenta will make sure she's naked in front of as many people as possible. You'd think she would stop getting up on stage anywhere.
Also, every episode deals with the faculty and students traveling to exotic locations, getting involved in weird mysteries, or getting involved in grand schemes. One has to wonder when they found the time to actually teach/receive an education.
Seinfeld Is Unfunny: While it has no doubt been eclipsed by other, more modern series, this is one of the Ur Examples of ecchi anime. Despite its nudity, it was rarely sexual in nature. It's essentially a typical children's cartoon that somehow revolves around a woman having her breasts exposed, as odd as that may sound.