Aaron Bailey is Michelle's recurring classmate. He is the typical class bully, who tends to be annoying and rude (especially towards the members in the Tanner household) at times. He pinches Michelle in the season four episode "A Pinch for a Pinch" when they are in preschool, and Jesse tells Michelle to fight back. When the teacher gives them both a time-out, Jesse takes Michelle home. While that behavior is discontinued, his obnoxious ways do continue throughout the series.
Eventually, Aaron becomes good friends with Michelle and is accepted into the group of friends, despite his being a little bit of a pest. In the Season 8 episode, I've Got a Secret, he does not want to swallow his pride and admit that he likes Michelle (until Lisa gives him an elbow in the ribs).
Danny even remarks in a season seven episode that they are watching Aaron for several days "until his regular babysitter stops twitching". Aaron's last appearance is in season eight's "Dateless in San Francisco".