The Cell saga ended with a twist that resulted in Goku's death and Gohan's victory. Peace returned to Earth and the curtain rose on a new scenario of dragon ball, featuring the latest saga, that of Majin Buu. Gohan had almost given up his career as a fighter, limiting himself to a few saves.
If he had stopped growing, the same could not be said of his brother. The new generation of Saiyans that arrived, that of Goten and Trunks, had much greater potential than the previous one. In fact, the young Goten was able to transform into a Super Saiyan from an early age, beating all the records set by his predecessors. But that transformation was also a weird scene with Chi-Chi.
Because Goten transforms into a Super Saiyan for the first time in Dragon Ball Z, Chi-Chi tells him that he has become a goon? This has to do with the Japanese culture and their facial features: all Japanese have naturally black or at least dark brown hair, so a slightly lighter color is very noticeable. So in the 80's and 90's, but still in certain contexts today, the blond Japanese were people who dyed their hair and basically they wanted to rebel against Japanese society.
Very often these would then become thugs, thugs, bosozoku, and more. That's why Chi-Chi says this sentence when Goten pulls out his Blonde Super Saiyan Hair instead of the blacks he was born with. Now Goten is growing up and we will see him in a different way in the superhero movie.