Insupportable translates to "unbearable" or "intolerable." It's an engaging word that captures a strong emotion and isn't heard in every French song.
In the context of the song, Vitaa declares, "Ça y est, j'vais passer en mode insupportable" (That's it, I'm going into unbearable mode). She uses this word to assert her independence and defiance, suggesting she's done with conforming and is ready to be unapologetically herself, even if it means being perceived as difficult or 'unbearable' by others. This makes it a powerful and memorable word in the song.
"Insupportables" is Vitaa and Slimane's answer to anyone trying to run their life for them. The whole song circles one refusal, repeated until it becomes the title: "Ne me prends pas la tête" [Don't bother me], "Ne m'dis pas c'que j'dois faire" [Don't tell me what to do]. Nobody is waiting for permission here, and the hook spells out where that attitude lands: "Ça y est, j'vais passer en mode insupportable" [Here, I'm going to become unbearable].
The verses back it up with small, concrete pictures instead of big declarations. There's a rocket taking off in someone's head, "Une fusée dans l'cerveau" [A rocket in my brain], headed for another galaxy so they don't have to sit through anyone else's story. There's "Deux-trois verres sous l'chapeau" [Two or three drinks under my hat] and a flat refusal to keep arguing about it: "Soit tu crèves, soit tu mords" [Either you die, or you bite]. It isn't really about being difficult. It's about being done explaining yourself.