Dash Dawson was in the episode "Super Nerd Much?" He stole the Cat's Eye Emerald, a gemstone that allowed him to steal "coolness" from others. With the ring on his finger he comes across as narcissistic and self-absorbed as while thinking he is about to escape, he tells the spies that he will "see them in their dreams", clearly believing that he is someone to be dreaming of and longing for.
During the fight where Arnold Jackson accidentally gains the Cat's Eye Emerald and turns Sam, Clover, and Alexandra into nerds, he assists the girls in stopping him. He and Arnold fight at the top of a blimp for the emerald.
After the Cat's Eye Emerald is finally destroyed, he is arrested by WOOHP and Arnold's memories of the incident are erased and he returns back to school as his former, nerdy self.
Samantha calls Dash the "dreamy-looking bandit" while telling Jerry that they accidentally dropped him in the bay during their fight. As Dash still appeared somewhat handsome; albeit looking perhaps a little less muscular and acting less quirky after being hit by the ring's power and having its effect wear off, it is most likely that Dash was just using the ring to enhance his natural good looks or muscle tone or gain more confidence instead of completely transforming himself from being a total nerd into a hunk like Arnold did.