The series revolves around Miss Machiko Mai, a new elementary school teacher who wears a revealing red mini-skirt, and regularly finding herself in accidental sexual situations. Machiko is very popular with her students, especially the boys, who take delight in lifting up her skirts and devising traps to catch her in various stages of undress. Rather than get angry, Machiko responds by laughing it off and uttering her trademark phrase, "Maicchingu!" (roughly meaning "Embarrassing"). Machiko is generally a very kind and patient woman who cares about her students and does her best to help them with their problems.

Source: Wikipedia