New Oxford Dictionary entry reads:
Clown’s pie (n). A very, very wet minge. “Finding ourselves alone in the shooting lodge at Balmoral, Her Majesty bade me descend to her ladygarden. After 50 years of widowhood, I found her to be considerably aroused. It was like being hit in the face with a clown’s pie”. (From”The memoirs of Queen Victoria’s Ghyllie” by John Brown )