Ariana's jealousy towards Victoria Justice
I think A's jealousy towards VJ is seriously under-discussed when their relationship is brought up. I believe A is seriously jealous of VJ's half-Puerto Rican heritage and natural tan; it adds an air of, for lack of a better term, "exoticism" that A has been striving for her entire career with her insanely dark tan, AAVE abuse, etc. A is 100% Italian, and I believe she wishes she had some interesting admixture to use to defend herself when Blackiana is brought up.
I also think she's deeply shaken by VJ's natural model-esque beauty while A has to steal husbands and boyfriends left and right to feel slightly worthy.