Schuyler
If some of the care staff who'd cared for one of my late relatives had vented in the staffroom about a "miserable old git" then I honestly wouldnt have cared. At times their actions and words were draining and we'd often felt similar as family.
People are human and humans get exasperated and have rubbish days.
I wouldn't ever approve of personal comments about someone's physical appearance as that's nasty and unpleasant, but if someone vents about a series of behaviours then I couldn't get wound up about it.
Put it this way, if I had 2 hypothetical colleagues:
Colleague A: Has had a rubbish day and last lesson 3/4 known hobby students have gone for them, actively ruined his lesson and they've had to call behaviour support to remove so they can actually teach the rest of the class who are lovely. They come into the staff room and declare they've really had enough of dealing with entitled little shits who ruin it for the rest of the students and how annoyed they are that a certain clique seem to be untouchable.
Colleague B: Spends every day on low level moaning, oh they have that y9 and "we'll see if they actually do anything today", then they've had to follow up a pastoral issue but "what's the point because they'll be over it long before anything happens". Never says anything really untoward but has a manner and way of speaking about the students that shows they couldnt care less and views them as an inconvenience.
I'd have more sympathy with A and would be willing to bet A is the better teacher. Sure,A off loaded and swore behind close doors, but it comes from a place of wanting to educate and being fed up with dealing with bratty behaviour that ruins it for the majority. B, on the other hand, never actually says anything that bad, but they don't actually give a damn about the students, they don't seem to enjoy being with them etc