reputation

[Grey Roger]

Depends on your definition of "quick". Killing an item trader drops your reputation and also triggers a big fight.

Another way to foul up your reputation is to attack a ship while flying a friendly flag. Again, this is not advisable unless you're ready to deal with the immediate consequence, which is finishing the battle against that ship and any friends it may have.

 

[Pieter Boelen]

Depends on your definition of "quick". Killing an item trader drops your reputation and also triggers a big fight.

It quickly drops your reputation. And gets you into trouble equally quickly.

Another way to foul up your reputation is to attack a ship while flying a friendly flag. Again, this is not advisable unless you're ready to deal with the immediate consequence, which is finishing the battle against that ship and any friends it may have.

I can't remember if that still affects reputation; we've gone back and forth on that quite a bit.
What I do know for sure is that completing an attack by sinking/capturing a ship while still flying a flag friendly to that ship does have severe effects on your Nation Relations.

 

[Grey Roger]

I'm pretty sure my reputation dropped rapidly when, during a playthrough of "Tales of a Sea Hawk" under the 28th July version plus fixes, I was trying to escape Speightstown in Rabel Yverneau's ship and fired back at the ships attacking me without remembering to change flag first. (Your flag has been auto-hoisted to French, the ships attacking you are French, so the penalty applied.)

 

[Pieter Boelen]

I'm pretty sure my reputation dropped rapidly when, during a playthrough of "Tales of a Sea Hawk" under the 28th July version plus fixes, I was trying to escape Speightstown in Rabel Yverneau's ship and fired back at the ships attacking me without remembering to change flag first. (Your flag has been auto-hoisted to French, the ships attacking you are French, so the penalty applied.)

Then probably something still remained. I wished I could remember, but it changed so many times that I just can't recall.
Relevant code is somewhere in the SEA_AI folder though; that much I do know.

 

[Talisman]

So, how to actually one captain can lower reputation?

Do the "Hard Labors of an Assassin" sidequest - Hard Labors of an Assassin | PiratesAhoy!

Your reputation drops by one level for each of the targets that you kill.