My Barbaric Girlfriend

Two teens see how the other half lives!
When her mad scientist grandfather accidentally switches their bodies. Akira Uehara is mortified when his best buddy starts hitting on "him," and is embarrassed to look at "himself" in the mirror in her underwear! He can't wait to get back to being a boy. But Nanako Momoi has other ideas--she is starting to enjoy life in Akira's body!
From Tokyopop:
Rude girl and effeminate boy switch bodies and find that it might be a better fit for both of them. Lots of crazy comedy. Nanako Momoi is the belle of high school... as long as she stays quiet. Once she shows her true self, guys' dreams are shattered for she is a true tomboy. Akira Uehara has the looks and brains, but, unfortunately, his personality is so dull it overcasts a shadow, and nobody notices him. One day, Nanako's grandfather comes up with a crazy invention, and Nanako and Akira trade Bodies! She's him, and he's her!