Pie-faced means “having a round, smooth, or blank face.”
Wellllll, I sorta hoped no one else would really notice, but…
For a full explaination of the dynamics involved in “a pie in the face,” one need go no further than Monty Python at the Hollywood Bowl. 
Classic.
I’ve thought about this, too. I think pies stand alone in slapstick. While slapstick can be anything from falling down to getting hit with a bucket of water, pies present a special comic element. It makes an adult look like a baby with food all over their face. Maybe all slapstick - falling down, pants falling down, makes adults look like little babies, which is embarrassing and funny. So there’s the sight gag of seeing an adult with a food mess all over their face, then there is the humor which comes from knowing someone feels embarrassed. I don’t think its humiliation, which implies shame to me, I think its just intense embarrassment, particularly if a lot of people witness the pieing, and are laughing at the victim.
(Of course, it doesn’t really matter what caused it, anytime everyone is pointing and laughing at you, its going to be embarrassing.)
But that’s the point, anytime people know you’re embarrassed from anything they are going to laugh at your emotional state. You can take a little comfort in knowing no one could find it funny if they hadn’t felt the awkward sting of embarrassment themselves! At the end of the day, its really a human bonding thing I think. Since everyone has been embarrassed at one time or another, they love to see they aren’t alone! Everyone acknowledges we can all lose control of our situation and our emotions. That’s what makes us human. So the next time you see someone get a pie in the face - laugh your head off guilt free! Especially if its you.
This seems like the most wrong way to go about it. Yes we all get embarrassed by something out of our control and it’s a shitty feeling, even if practically anyone witnessed it, never mind if people saw it and were laughing their asses off at me and my humiliation.
It’s a shitty feeling to be embarrassed and if I have anything resembling positive feelings for the person being embarrassed or humiliated, it won’t be something I’m laughing at.
Because pies in the face have become cliched (as early as 1964 Stanley Kubrick chose to excise an extended and expensively filmed pastry-throwing sequence from Dr. Strangelove), modern comedy has had to search for other food substitutes.
I’m just not finding the humiliation or embarassment in pie throwing. Hardly anybody gets hit in the face with pies in real life. Unless it’s a publicity stunt or a prank being posted on YouTube these days. And how often do those happen? And the people who got hit with pies in old movies or in Vaudeville were willing participants in an entertainment. Or in the Three Stooges remake or in a sitcom. It’s imaginary humiliation, so what’s wrong with laughing?