"Dorodo" is an inside-joke between TheMidnightFrogs. It originates from Fatty Time Episode 4 back in December 30, 2009, wherein Yoshi played various bad auditions for Sgt Frog fan projects. One of these was of a young boy auditioning for Dororo, but acting generally idiotic and forgetting to actually audition for the role. Early in the video he mispronounces Dororo as "Dorodo", (also calling him "Doro-do something"). The team's resulting hysterical laughter at the video solidified "Dorodo" as an inside-joke between the team.
"Dorodo" became the earliest example of getting Dororo's name wrong, a classic running gag involving the character in Sgt Frog Abridged. While "Dorodo" was not specifically used in the series until SFA14, "Zerodo" (a variation using Dororo's birth name, Zeroro) was used earlier in SFA2R and SFA7.