There's, to me, no obvious clear cut line. But here are some indicators that make me consider someone was being grossly negligent and/or even malicious:

- ignoring warnings

- acting against known-to-them best practices

- repeating a previous mistake

But, again, these are just indicators, not a checklist.

Interestingly, any of these can happen also due to stress, burnout and generally broken company/team culture. Including something like a CYA culture where if they don't do something fast, they will be blamed for it, and thus they need to move fast and break things.