"Shoo" - traditional term for getting rid of an unwanted animal.
Main Entry: 1 - shoo
Pronunciation: \ˈshü\
Function: interjection
Etymology: Middle English schowe
Date: 15th century
—used especially in driving away an unwanted animal
Two shoes thrown at a press conference have a symbolism similar to those tied behind vehicles used to depart a wedding. They are a fertility symbol, and the person who launches them is trying to suggest to the target that he "get screwed".
"Shoes tied to the bumper of a car hark back to the days when shoes were thrown at the bridal couple to ensure fertility. Shoes are said to have been a fertility booster because the foot was a powerful phallic symbol."