In a direct, positive manner
In a rapid way
Completely such, without qualification or exception
He actually flat-out stated it.
Sofia hung up and stared at the number on the paper, wondering if Jake had lied to her or if he flat out screwed up the number.
He flat out refused to go out after dark last night.
No one wanted a dying girlfriend, especially when she'd flat out refused to marry him.
The second soul bartered for in private was flat out missing.