A fun thing happened... I was after the diplomatic victory achievement and thought I had nailed it when I had 8 out of 10 diplomatic victory points and > 1200 diplomatic capital right before the final vote, with nobody else coming even close. However, I was only able to create 16 (expensive) upvotes for myself, whereas my rivals combined their powers and voted against me, amassing 21 (inexpensive) votes against me!
I was playing as Sweden, and only Eleanor of France voted for herself, being able to come up with only 4 votes. So, 20 for, 21 against. :( I was a bit pissed to say the least.
I tried reloading my save and buying the diplomatic favor out of my competitors, but they would not give me a single point of it, no matter what I offered them. Then it hit me: I only needed 22 votes for, no matter to whom, but my votes would dominate the vote. So I did a counter-intuitive thing: I gave Eleanor a gift of 140 diplomatic points, which allowed her to buy 3 extra votes for herself whereas I only lost 1 vote by doing that. And lo and behold, trying the vote again: 22 votes for giving 2 victory points to a player (15 for me, 7 for Eleanor) and 21 votes for deducting 1 victory point from me! :D