Dean is a boy who vacationed to Little Pwagmattasquarmsettport with his family.
While there, he met Lisa Simpson, whose family was also on vacation and had the intention of making new friends and leaving her nerdy self back in Springfield. By acting like her brother Bart, Lisa immediately clicked with them and takes them skateboarding at the library.
Bart discovered she's acting like him and decided to try to steal her friends. He first showed off his skateboarding moves to try and impress them, but he failed. Erin asked Lisa who that was; she replied that he was her dorky brother Bartholomew, making sure she didn't use his nickname 'Bart'. Then he showed them Lisa's yearbook (which has all of Lisa's nerdy accomplishments) and Lisa, assuming they won't like her anymore, runs off crying. However, Dean and the group realized that Lisa is a good person and they glue shells on the family car that say "Lisa Rules." They also signed her yearbook.
- The male kids Lisa hangs out with are named Ben, Dean and Rick, but they don't specify who is who, so it is uncertain if this boy's name is Dean actually.