A new and better UN
Looking at the preamble of the UN charter one would be hard pressed to assert that the UN has not been a total failure.
A lot of the reason is overreaching on the UN's part, and also the whole concept that just giving lip service to concepts such as freedom and human dignity will make a country better.
It is similar to various gun laws in the US. "I was going to go on a shooting spree, but it is against the law for me to carry a gun within 500 yards of a school, so I guess I am out of luck
If you are inclined (as a person or a country) to act in a responsible way then all the laws or agreements in the world will not change that inclination. Witness all of the members of the UN various human rights committees with appalling human rights records.
That being said, here is the "Replace the UN with the Phil-UN plan."
1) The following criteria must be met to be a member of the Phil-UN:
a) No member country may have the same leader for more then 12 years.
b) The leadership of the country will be elected.
c) Citizens shall have the ability to freely emigrate.
d) The press shall have the right to print whatever it desires.
2) Countries belonging to the Phil-UN shall be required to set tariffs on imported/exported goods as follows:
a) All goods traded with member countries shall have incoming and outgoing tariffs of not more then 5%.
b) All goods traded with non-member countries will have a tariff of not less then 10%.
c) Any country making war on a member country shall be expelled.
d) Some token amount (say .01 gdp) goes to support health issues (anti malaria, anti diarrhea, clean water, etc).
After that, maybe the countries who do not meet the criteria to be in my UN can form their own. I can see Castro, Ahmadinejad, Kim Jong Il et. al. setting up an anti-UN with the following rules:
1) All media shall be government owned, and print only what the great leader decrees.
2) The people shall be free to vote for anyone they choose, as long as they choose the great leader, and understand if they write in a candidate all of their fingernails and toenails shall be removed via red hot pliers.
3) The people shall be required to "donate" their time for the construction and upkeep of the dear leaders various palaces, as well as supplying any young girls they might have for "service" within said palaces.
4) Other rules shall be unwritten, but the great leader and his secret police will be sure to let you know if you transgress on them.