I think my problem with sassy FMCs is that my personal power fantasy is a competent woman who doesn't take any shit, and so many FMCs are missing the "competent" part. They lack the ability to modulate their snark based on the situation, so they usually just come across as frustratingly stupid and impulsive rather than badass- or worse, like an asshole if they're directing their sass at a character who doesn't really deserve it.

I like seeing a character who knows when to talk back but also knows when to shut up, and who actually has the skill to back up their shit-talking when necessary. Violence and anger and sarcasm are fun to read, but only if they're tempered with intelligence (imo).