Midori Days (Inoue Kazurou)

This is a pretty funny manga. there's actually some ecchi stuff in here but skip that and you'll see yourself laughing like hell at their actions. xD
story-
Summary: (From Mangafox.com)
Seiji Sawamura is the toughest seventeen-year-old in town, feared by all for his fighting prowess and his deadly "devil's right hand." But at heart, Seiji is a softy, and all he wants is an end to his seventeen-year history of being a lonely single guy. Unfortunately his tough-guy reputation only serves to decrease his popularity with the ladies. However, what happens when Midori, the only girl who actually has a crush on him, replaces his "devil's right hand?"