To have egg on one's face means to look foolish or be embarassed. For example: You'll end up with egg on your face if you continue nagging me.

There can be benefits to using the white part of an egg on a persons face. Using egg whites may prevent wrinkling, acne, and keep the face feeling and looking smooth.

They had egg on their faces. (plural.)

To have "egg on your face" means to be embarrassed. Like "I messed up completely and now I have egg on my face." If you "had egg on your face" it means that you were caught doing something you should not have been doing. The image is of a fox or cat who has been chasing the chickens and eating their eggs, trying to pretend they are innocent when they have the egg all over their face where they were eating.

The face that sperm cannot live long, and only one sperm can fertilize egg at one time.