Seitokai Yakuindomo, Oshiete! Galko-chan Recommendations
Both use dirty and sexy humour.
Sex positive, occasionally witty, and dripping with indecency. Both shows consist of a core cast of girls with coarse senses of humour shooting dirty jokes one load after another, hard and fast.
Whilst common anime tropes such the innocent Ojou-sama character is subverted in both series; Seitokai Yakuindomo more or less follows popular manzai comedy traditions whereas Gyaruko-chan relies more heavily on trope subversion, frank realism, and situational comedy.
These two anime have similar formats, in that they consist largely of brief comedy sketches and gags strung together into episodes, and have a small group of high schoolers as their main cast with numerous supporting characters. In both cases, the subject matter is often sexual and includes topics that are taboo (at least by western standards), such as feminine hygiene. Of the two, Seitokai Yakuindomo has more perverted characters and topics.