I know this is sort of an odd question, but I'm curious as to why a pie to the face is so closely tied to comedy, specifically to clowns.
The story is that the first pie was thrown as an impromptu action between actors in 1913. A top exec at Keystone Studio happened to see it, liked it, and pie throwing became a signature of their movies.
Of course, once one studio has a great bit then other studios will copy and expand on it. Soon just throwing one pie wasn't enough. Each studio tried to top others with more involved pie mayhem.