I can’t believe no one has asked this on this before (on the SMDB), but does anyone have any idea where this phrase came from?
Well, according to this page:
Meaning: To pretend to be serious while joking
Origin: Comes from the practice of biting your tongue causing pain in an effort to suppress laughter or a smile. If you bite your tongue with your side teeth you have put your tongue in your cheek.
I’ve heard similar explanations elsewhere.
Plus, saying “eyes firmly rolled” doesn’t have the same oomph.
According to http://www.wordorgins.com it means: