A man makes a comical reference to porn sites, saying that another man got a sprain in his shoulder from clicking on them too much.
A teen boy is falsely accused of stealing several girls' recorder reeds to lick them. Several other boys are also falsely accused of stealing girls' gym clothes.
In the second episode of season two, there's a pervert who goes around wearing a raincoat but nothing else, but nothing is shown. At one point, he trips and falls over and we see his buttocks. He is stopped in the end and the scene is brief.
In several episodes, male characters' buttocks are seen, usually under comedic circumstances of accidentally losing their clothes. The show's art style is rather cartoony, though, so this isn't as offensive as it could have been.
The second season has some stronger sexual references than the first season and it can hurt the senses and make the viewer uncomfortable. Instead, all these references are censored in CN LA and Brazil.
The Season 1 has mildly sexual innuendo and references. Much tamer than the later seasons.
In season 1 episode 6 a male student accidentally slides under a teenage girl's skirt, showcasing a view up her skirt and shirt with a detailed image of her panties (labia outlines visible) and bottom of her bra. The scene is accompanied by an "oh yeah" moaning sound and a sensual image of the girl's mouth, which is then followed by a high-pitched scream.