About

Pieing (Also known as Pie to the Face or Pie Fights) is a slapstick act in which one or many participants throw a pie at another persons face.

Origin

In the the silent comedy Mr. Flip, a man goes around town trying to flirt with various women, always winding up getting hurt in some way shape or form. The film climaxed with a waitress throwing a pie at the mans face.

Spread

In 1913, filmaker Mack Sennett became well known for including at least one pie throwing scene in his films.

From Wikipedia:
At least a half dozen films have been made incorporating extended pie-throwing battles. The first was Charlie Chaplin's Behind the Screen released in 1916. The definitive pie fight film is The Battle of the Century (1927) starring Stan Laurel and Oliver Hardy, using 3,000 pies. Our Gang's Shivering Shakespeare (1930) winds up with an auditorium full of people throwing pies. The 1935 short subject called Keystone Hotel featured a large pie fight ending with the camera taking a pie. In 1941, another major pie fight film appeared: The Three Stooges' In the Sweet Pie and Pie. A Technicolor film involving pies was the 1965 comedy, The Great Race; known for having the largest pie fight in cinematic history. Its $200,000 pie fight scene used one large cake and 4,000 pies, and took five days to shoot.

Pie Throwing became a common activity in the Looney Toons and Monty Python series as well.