Arab terrorists hurl rocks
The easiest solution is for the US to propose to China and Russia that they build their own UN headquarters, and that the UN can rotate from HQ to HQ every decade. They will likely jump at the opportunity, thinking it would give them “prestige” (snicker).
Then, after the first rotation, the US should propose, “to be fair”, that additional UN headquarters buildings be built:
In the slums of Rio de Janeiro, or Brasilia, Brazil, for South America; Harare, Zimbabwe or Mogadishu, Somalia, for Africa; and Riyadh, Saudi Arabia, for the Middle East.
This means that it would be 50 or 60 years before the UN could again set foot in the US. I think we can all live with that.