Harry yanked his robes straight and headed for a seat at the very back of the class, where he busied himself with piling all seven of Lockhart's books in front of him, so that he could avoid looking at the real thing(refers to Lockhart).
“You could've fried an egg on your face,” said Ron.
“You'd better hope Creevey doesn't meet Ginny, or they'll be starting a Harry Potter fan club.”
“Shut up,” snapped Harry.
The last thing he needed was for Lockhart to hear the phrase “Harry Potter fan club.”
I don't quite get the meaning of “You could've fried an egg on your face,”. I think it's a metaphor. The close phrase I can get is "have egg on one's face", which means: Fig. to be embarrassed by something one has done. But the phrase "fried an egg on your face" might be different. What does it mean exactly? Is it the same as have egg on one's face?
-- From Harry Potter and the Chamber of Secrets.