A fork of Rural Dictionary
Originally the phrase mean a less than enthusiastic blowjob; you know, something that gets the job down but leaves all parties feeling dissatisfied. But in contemporary parlance it can signify a lazy or dispassionate attempt to accomplish a mission or assigned objective.
Original meaning:
After a John visits a mediocre prostitute: "I gave that bitch a 10 for that downtown charlie brown."
Contemporary meaning:
After a manager scolds his employees for idleness: "Man, y'all some downtown charlie brown-ass mothahfuckahs."