Interesting that war is a rare thing for you. Perhaps you have completely mastered Diplo?
The Germany example I mentioned had buffs for DoF, returning civilians, trading, they had my religion in all their cities, war together against common foe, i gave them host of WC, voted for their proposals, etc.
Then they TRIPLE citadel-bombed me! and were clearly ready to DoW with 6-7 Infantry on my border.
Since you seem to know more than me, what exactly is the score with plotting reports. How accurate are the AIs about each other's intentions. When I first started playing the game I assumed it was fact reporting. But lately I've begun to feel that it's 50:50 at best. What do you think?
If you look at any website for the strength of diplo modifiers, I can tell you EASILY that warmonger penalty can be stronger than 4-5 buffs combined depending on your warmongering.
Other than that I can think of other red buffs:
You made a friendship with their enemy
You denounced one of their friends
You DoW'd or denounced a friend
You told a civ you weren't going to attack them (doesn't have to be Germany) but did it anyway (this one is rather extreme)
You broke a promise (spying, purchasing land, settling)
They covet lands (most likely cause of citadel bomb)
It won't matter if you have 5 green buffs (in reality though I think it's only 3 that are bright green, as the religion buff goes away and if the trade deal is not heavily favorable for them it will also be faint green; voting for their proposal only lasts 15 turns however and the strength of the buff is rather weak... voting them to be host gives you a positive diplo around half the strength of a DoF) if you have a similar number of red debuffs
anyway take a screenshot... I can hardly believe that they'd do that with just 5 green buffs and no red buffs. (the AI is coded to view each player as either enemy, competitor, friend or ally; I'm sure for example, if you have DoF, mutual friends, WC host, landmark, and perhaps a liberation buff, they will view you as ally, hence 0% war regardless of army size assuming an average AI's flavor, unless bribed of course)