Murky said:
Raze the city where the U.N. is located?
FYI, razing the city only removes the actual building. Votes will still proceed as normal as if the UN was still there.
Additionally, capturing the UN bestows the same benfits as building it in the first place. So whoever controls the UN will always be one of the candidates for the elections (vs. the most populous of the remaining civs).
And if you turn off the diplomatic victory condition, the UN isn't available to be built at all, so no votes will occur.
The only way you can ensure NPT gets overturned is to have enough votes to overturn it yourself. Which means you need to have 51% of the total world population. Ironically, the easiest way to give yourself controlling intrest in the UN is nuke the bajesus out of everyone else, reducing their population.
So if you want to play with Diplomacy on, and ensure no NPT is ever passed, you have to make sure you build the UN and get elected as Sec. General, which means you will have to play nice up to the point that you have the nukes so the AI civs will vote for you. Once you start nuking, you're virtually assured of losing the S.G. vote the next time around as everyone will be pissed, (unless you have the afore mentioned 51% population to vote yourself back in). A rather nice catch-22 I think.