To have such a day would be a great idea but how to get it internationally agreed and publicised is perhaps not so easy.
Eh, just make up a date, claim that it was by international agreement, and start a chain email. Those things are virtually always accepted as truth, circulated for years by people who can't stop forwarding email to their entire address book, and eventually they reach the entire world. Give it a try; your great-grandchildren may one day be forwarding the same email.