Justin Jake Ashton is a teenage actor/singer that Vicky believes to be her boyfriend, but this was just Mark Chang using his fake-i-fier.
Justin Jake Ashton is a human celebrity that is a pop sensation between the teenagers of Dimmsdale (and maybe of all the U.S.A.).
He has blond hair and wears a green shirt with a long white sleeve shirt under it.
In King Chang, Mark reveals that he usually uses his Fake-i-fier to make Vicky believe that he's Justin Jake Ashton, the teenager idol. On the end of the episode, Vicky broke up with Justin (Mark)
In Sooper Poof, Mark disguises himself as Justin again after Timmy wishes for the Fake-i-fier to be fixed.
In Fairly OddPet, Vicky says she got in a fight with him and refers to him as her boyfriend, possibly indicating that they have reconciled since the fake-i-fier incident, but are now in a rocky relationship.