There are probably a million caveats I could put in this thread / on this topic, but I'll keep it to just a few thoughts.
Generally, I tend to be extremely reluctant to give advice. irl I predominantly listen, and I am not one to start giving a monologue or unasked-for opinion on anything... I just state a few [probably bland] generalities and tend not to give explicit thoughts on what a person should or should not do. That's just about the last thing I would do. Even if people ask for advice (which really doesn't happen that often), I tend to be hesitant, because I am usually of the opinion that at the end of the day, people don't really want advice and will end up doing their own thing / change their situation when THEY are ready. My giving them an alternative / my perspective is only as good as whether they're in a mental space to actually be willing to hear that or be receptive to that; and often-times I just rarely sense that people are in that space where they're actually open to what I might have to say. So, I simply listen, or if people are in that in-between zone, I might insert my bland generality / thought, to maybe try to get them along the road of thinking in a different perspective, but that's about it. Most of the time it seems people just want to vent their own self/thoughts out, and just want someone to actually *listen* to them, so I do that. And, often-times, I think I don't have much wisdom to offer, as I am always concerned about projecting my own self onto them. So, this too results in my doing tons of listening about a particular situation, until I feel I have enough information to give them a personalized thought - not just a blanket thought, since many blanket things may not apply, given that person and where they're that.
If people ask for critique, I'll give critique. Some people like that, and if I know they like that, I'll present the critiques. Also, depending on the environment (i.e. work vs. personal relationships), I can go into that mode, or not. I also like to give praise and encouragement. If it's not genuine, I'm not about to say anything.
Receiving criticism? I don't know. I think a lot of the time I'm able to just factor in WHO the person is who is critiquing me; if I know they're the sort of person who naturally critiques and it's nothing personal, I don't really take critique badly from them, and treat it objectively. I guess initial thought is that I think I'm able to detach fairly well when it comes to critiques - like, I have a subjective/personal view of myself, and can also step back and view myself objectively, and very well might agree with the critique (because I've very likely critiqued myself already about that very thing).
As to the premise of the OP -•When it’s OK to complain about someone else to a third party.
•When venting crosses the line and become a malicious attack.
I think people of ALL types complain and vent. Gossiping ('malicious' 3rd party discussion?) occurs across the board for all types, although everyone is going to have their own notion of what is and is not 'ok' to gossip about, and what's 'good' or 'bad' to talk to someone else about, but everyone still does it, and all types will complain about one thing or another to trusted people.