What is Fix That Lip?
1.
Expression directed toward an individual when he or she is not getting their way, and so they pout their lower lip.
Also used when someone is noticably sad faced and you don't want to see it.
A phrase to get someone to "man up" and quit being a baby.
son - "Can i have my way today?"
father - "No."
...
Father - "You better fix that lip, boy!"
See