A lo-bo was a type of person described by Officer Foley. In 2015, Hilldale was known to be full of them.
Behind the scenes
It is possible this is the equivalent of a "hobo"; or someone who has damaged their brain (through abuse of drugs or bionic implants) equivalent to a lobotomy; or that it's similar to the "low-res scumbag", referring to someone with low standards or low intelligence. The term was part of the 2015 slang that was left to the imagination of fans of the film.