The quality of being slouchy, or having a drooping or lazy posture.
Slouchinesses is usually seen as a bad thing because it shows laziness or lack of care.
Examples:
His slouchinesses made him look tired.
She always sits with slouchinesses.
The slouchinesses of the cat made it look very relaxed.
The slouchinesses of the tree branches made them look sad.
The slouchinesses of the old scarecrow made it look spooky.
The slouchinesses of the puppet made it look funny.