From MopedWiki

"Get fun!" is a phrase that was popularized by Peddy Cash/Team Mayhem member, "Downtown" Joel Brown (who also has the maxim tattooed in hot pink on his knuckles). "Get fun" is defined as having a good time, above all things, and making it a lifestyle. This infectious battle cry spread to the Mosquito Fleet via 2005's Kalamazoo BBQ, and was summarily brought back to Seattle. Months later, the phrase evolved into, "Get fun, bitches!" during Seattle's 2005 Blood DriveIII, and has remained popular among Seattle Fleeters.