If something is slouchy, it is loose and not straight. Also, if a person is slouchy, they are sitting or standing with a bent back and shoulders.
Slouchy can make people think of being lazy or not caring much about how they look.
Examples:
Her sweater is slouchy and comfortable.
He wore slouchy pants to the party.
The slouchy hat fell over his eyes.
The cat looked slouchy as it lay on the couch.
She always looks slouchy when she's tired.
The tree looked slouchy in the wind.