Learn English – Origin of “egg on the face”

It often implies that you have made a serious mistake, but more strictly it indicates that something you have done (or some turn of events) has left you looking embarrassed or foolish:

Murray knows all about the Chilean 12th seed — he practised with him last week — and the British number one realises he could be left with egg on his face if he leaves Gonzalez an easy, mid-court ball.

Where it came from (source):

I know of two suggestions for where it came from. The late John Ciardi suggested an origin in the lower-class and more rowdy kind of theatrical performance, in which an incompetent actor would have been pelted with eggs and forced off the stage. The other is that it was a comment on a minor social gaffe at a meal, when poor manners or sloppy eating left egg around your mouth.

And also (source):

From the embarrassment suffered if the yellow yolk is on ones lips or beard after eating a soft boiled egg in one of those egg cups, a favorite breakfast of the upper crust... Yellow egg shows up especially well on a beard or mustache.