Criteria varies. Red flags (such as loads of flagged comments here), name calling, threats, "bad" things.
Once and applicant was dismissed from my process because their comments on social (not just HN) showed a severe distaste for "n00b JS". The position clearly identified use of these tools. The demonstrated attitude would be caustic to my team and my junior devs would suffer.
Since companies always have more applicants than jobs we can be choosy. I filter for social fit first.
I can teach you to code. I don't know how to teach you to be respectful.
Again, HN profile is one of 100s of factors we compare on applicants
HN is a work-related profile for some jobs.
Hiring is already a minefield. HN or social profiles are just one way for either candidates or employers to blow themselves up.