Okay, I Thought I Did, But it Turns Out I Don't...

I'm not sure I have ever seen this, but if you mouse over their planet in the diplomacy screen it shows you all the modifiers to their attitude toward you. This doesn't have much flavor, if that is what you are looking for, but does give you the information.

Not sure either. I've only seen this in one game. and I did two things that could have caused it. One was exactly what you did, trade then go to war right after (not sure what the time limit on that is though, so maybe you traded with them a few turns earlier and forgot, but it still counts as "You know what you did...?). The only other thing I could attribute it to was that I stacked a bunch of fleets in their territory prior to DOW. Just thought of a third, unlikely possibility: attacking prior to DOW? I forget if I did that...

I also had thought that trading with someone and then declaring war on them without breaking off the trade first might do it but now I don't think so. I think trading with them for anything and then declaring war on them the very same turn will do it. Just taking stabs in the dark here...

I normally go to the diplomacy screen and hover my cursor over their planet icon and that gives the reasons why they don't like you or you could click on their planet icon and in the right hand profile click on their report button and the reasons are/were on their report page?

I fully understand that. I'm only talking about the "You know what you did" reason for not liking me. What causes that? This is what I'm trying to understand. I see it come up every now and then in my games and the reasons for it aren't fully clear to me. So I'm asking others, what causes the AI to list this reason why they don't like you?

I honestly don't know that either mate sorry

Hey, no worries. I should have been a bit more clear in my original post as to what I was asking. Off to edit it now...

It's called 'grudge'. Here's the relevant code:

I think the idea is for it to add a small stacking penalty to relations for every war you declare, with extra for breaking treaties. It times out eventually. 

On the other hand, like much of diplo, I'm not really convinced it works properly.

LOL I should have known that I should have just asked you. Thanks for the info. I think I may have a better idea now what triggers it. I never imaged it relating to the number of times I've declared war, which isn't a lot!