Albert Lau, Becky's uncle, saw my post on Loco Moco in Hawaiian Food, Part 2 - Local Style. He told me that he and his friends used to help out at a restaurant in Hilo. They got to asking for the combination of rice, hamburger, eggs, and brown gravy. This is what he wrote:
"It started at the old Kinoole Drive In. The word loco was named by the waitress who used to call us loco for ordering that dish. My friend, [the late] Herbert 'Shange' Asakura, asked her, 'Why don't you put it on the menu?' The waitress asked what we should call that dish. We all thought and Shange came up with the name moco since it sounded good. That how loco moco got its name."
The dish caught on, including, presumably, the Lincoln Grill, credited by Wikipedia for inventing the dish. According to Uncle Albert. Cafe 100 apparently trademarked the name, which is why loco moco is identified with that restaurant.
There you have it. Authentic oral (in every sense of the word) history! Thanks, Uncle Albert: I definitely think yours is the genuine story.