Sono Otoko, Wagamama Nitsuki

On her 17th birthday, high school senior Shiina tries to sneak with her friends in a very hip club run by an attractive guy named Makoto.
When she tells him her name, he seems surprised. However, upon learning her age, he kicks her out.
At school the next day, Shiina finds out that her geeky science teacher is actually Makoto in disguise!