Sensei Nante Kirai Desu.

Sensei Nante Kirai Desu. summary:

Ikuta Aoi has a crush on a girl in his class and tries to confess to her, but in his nervousness accidentally insults her. To make matters worse, the whole embarrassing scene is witnessed by Shizu sensei, the handsomest and most popular teacher in school...who also happens to be the object of Aoi's crush's affections. One thing leads to another, Aoi ends up speaking rudely to Shizu sensei, and from there on out finds himself being forced to run errands for him as penance...