If something is done scummily, it is done in a dirty or unpleasant way.
The word scummily has a bad feeling. It means something is not nice or clean.
Examples:
He cleaned his room scummily.
She ate her food scummily.
The dog licked its paws scummily.
He made his bed scummily, with toys all over it.
The witch's house was scummily decorated with spiderwebs and dust.
The boy scummily wiped his hands on his pants after eating.