Not a teacher.
"Embarrassed" seems to work. That's the point of the idiom, you go out into the world thinking you are presenting yourself as a competent, intelligent human being. Then you find out later that everyone is laughing at you because you have part of your breakfast all over your chin.
e.g. "He embarrassed himself when he thought he knew how to run that software" is one way to put it.
To say "He got egg all over his face in front of the client" is another, more colorful way.