The month of March has no fewer than 25 international days dedicated to a specific theme. The most well-known of them are March 8, which is International Women's Day, March 20, which is International Francophonie Day, and March 22, which is World Water Day.

But did you know that March 25 is International Procrastination Day? This day was celebrated for the first time in 2010.
 
The site Journee-mondiale.com counts 441 international days. The United Nations calendar has 119 international days. December 10 – Human Rights Day – was the first of them to be instituted, in 1950. Exactly two years before, on December 10, 1948, the U.N. General Assembly adopted the Universal Declaration of Human Rights.
 
Sources:
Wikipedia, Journée mondiale and United Nations.