Griefing is a term that varies amongst people and I think firstly, a defined stance needs to be confirmed on that. Like what @Thor-von-Blitz shared, if thats the definition everyone understands rather than personal varations then I think there can be better progress on this issue.
Theres nothing wrong with holding your ground, if you shoot first thats up to you and its up to the ship on the receiving end to decide on how to react. Sitting at outposts isnt griefing, its peoples foolishness for falling foul to that - That said on the topic of outposts and being occupied maybe just maybe have the inn have smoke coming out of it when the island is occupied and none when it isnt. No one can claim outpost camping from that, tbh I think theres enough indicators now but more obvious = less moaning. However, I personally think people just need to learn what to look for more.
What I do consider to be a pain is the relentless ship that you sunk that keeps coming back over and over every couple of minutes because they spawn within visible distance. Whilst doing a fort yest my crew when 4-0 against the same ship, they never stood a chance, it was brutally unfair but they kept coming back, they get fresh resources, we had to leave temporarily leave to get more and return. Thats annoying all round, they were severely outmatched which is no fun for them and boring for us having to deal with it every few minutes - It was mentioned before about the possibility of breaking ships apart and I think that needs implementing. The ending of the mermaid respawn cycle is great but now when a ship sinks it needs to disappear to the other end of the map, better yet a different instance entirely (but I can see that being mighty difficult to do with not all crew dying at the same time). That seperation is needed. if the losing crew wants to hunt them down, thats fine but itll take time to do so and on the flipside it allows a ship to escape the few that grief. Those that sink a ship, see it respawn and go to sink it again, and again, and again - Those are the griefers, theres no value in that.
This goes with the topic of death cost, and the mermaid respawn, if youve lost your ship, youre done, youre out, youve lost. So break it up, itll benefit everyone.
The brig system will be alot better when the crew numbers are fluid. Its already been mentioned the devs have a system in progress about locking a crew to 3 but a 4th can join by invite. That needs implementing quickly and itll solve alot of those issues.
I still think the solo sloop needs a "are you really damn sure?" because alot of the moaning is new players picking solo play having never played before. Its tough when you know what youre doing, nigh on impossible when youre new and so many are falling into that trap and then cry online about it.