Superlative form of the adjective 'sloppy', meaning the most messy or untidy.
The word 'sloppiest' can make people think of things that are not neat or clean.
Examples:
This is the sloppiest room I've ever seen.
She always wears the sloppiest clothes.
The sloppiest part of the house is the kitchen.
That was the sloppiest painting I've ever seen!
He made the sloppiest sandwich in the world.
The dog made the sloppiest mess on the floor.