Mooch Bart is Bart Simpson's adult form.
Future-Bart's hair has grown a bit scraggly, and he has tied some of it into a pony tail. A Hawaiian shirt, shorts, and sandals complete the "dressed down" look. He has inherited his father's physique, belly fat and all. He has sags under his eyes, and one earring
At age 40, Bart's gained swag as a poor guitarist and alcoholic that dropped out of the DeVry Institute. He lives in a ratty beach house alongside Ralph, the only other member of Bart's band. At this age, Bart acts like an especially spoiled version of his ten-year-old self, still calling on his mother to make Lisa play fair when she does things like telling him he can't join the presidency (Lisa is the President of the United States at the time). He mooches money off his parents and Ned Flanders, to whom Bart regards as a "softie". His new catchphrase: "You used to be cool, man." He says this whenever he hears something he doesn't like from someone. Bart continuously embarrasses Lisa and unwittingly ruins her tax plan to get out of debt. Surprisingly, Lisa is much more embarrassed of Bart than of Homer in this episode. In the end, however, Bart's extensive experience with evading debt collectors leads to him helping Lisa buy some time to pay off America's debt to other countries. In gratitude, Lisa legalizes "it", "it" likely being the use of cannabis.
In Holidays of Future Passed, Bart has two children, Jiff Simpson and Skippy Simpson, who he barely ever sees. Jenda is now his ex-wife and has married her new boyfriend. His children have to stay with Bart for Christmas, which they think is going to suck. He eventually teaches them the meaning of Christmas, which schools aren't allowed to do in this time period.
In Days of Future Future, Bart is working at Cretaceous Park and is sad that his love with Jenda haven't worked as expected and now he misses his kids. Nelson tries to convince him to be happy as he's a free man and dragged him to a party, where he's asked to leave. He then finds a brainwash clinic that helps him forget about Jenda. He manages to find other girlfriends, but he still misses Jenda. He later learns that her alien boyfriend, Jerry, has abandoned her. After a talk with Bart, she realizes that he's much more mature and decides to get back with him. As their second relationship wasn't working out either, they decide to break up again. He then wakes up at the clinic's chair and discovers that it was all a dream.