That's... delightful actually, an extreme rarity. I noticed relations were horrid before I refused the vote. We had been at war, I razed some outposts and used WMDs against them. Then I got another -10 (nice touch) modifier for refusing the vote, they are "furious".
I like to think that it was self preservation kicking in that caused this, they are completely outclassed by my empire. I know this is probably temporary, and if I pursue this session they will just declare war again at an opportune time, but I like the fact that this can occur, even if it is extremely rare.