It started with the mob that burst into the US embassy in 1979 taking 52 American hostages for 444 days. The hatred has lasted ever since.
Embassy wall climbing is now a favorite pastime in Iran. It builds character for the insecure, strengthens the Gluteus Maximus, is a wonderful social event, winning the hearts and minds of potential spouses.
Nothing to show the world how civil, law abiding, and evolved a country is, like climbing embassy walls and shouting slogans like a genuine Persian wild ass.