when vriska insulted and demeaned eridan, it made him want to fight back and prove her wrong and make himself better in order to spite her; their rivalry pushed them to be better than they were
when gamzee insults and demeans terezi, she feels like she deserves it and it serves no purpose except to push her lower and keep her trapped in a web of self-loathing and completely at his mercy
and that friends is the difference between a kismessisitude and abuse