I enjoy looking up the origins of words and phrases. For many years I took it as a truth that the Elephant and Castle was a corruption of Infanta de Castile, the Spanish princess who was engaged to King Charles I.
However, the prohibition of this marriage by the Church in the 1620s led to war with Spain so it seems unlikely to have been a popular name.
A more likely explanation is that the name derives from the arms of the Worshipful Company of Cutlers, the London trade guild which has an elephant carrying a castle-shaped howdah (lovely word in itself).
So what other common myths do you know about the origins of words and phrases?