Throwing a pie in a person's face has been a staple of film comedy since Ben Turpin received one in Mr. Flip in 1909, and is often associated with clowns in popular culture.
Clowns often throw pies in a person's face in movies. The first one to do this was Ben Turpin in 1909, in a move called Mr. Flip.  Now, clowns often due this as part of popular culture.