Definition
An expression used to tell someone not to worry, often considered condescending or offensive as it suggests the person is not intelligent enough to understand a particular matter.
"Don't worry your pretty little head about the details of this report; I will take care of it."
"The complicated parts of this project? Don't worry your pretty little head about them, just leave them to me!"
"You just focus on your job and don't worry your pretty little head about anything else."