1. most covered with or containing scum (foam or froth on a liquid surface)
2. most contemptible, worthless, or morally reprehensible
Usage: informal; derogatory

Examples

• The scummiest pond in the park was covered with green algae.
• That stagnant water looked like the scummiest mess I’d ever seen.
• He was known as the scummiest character in the neighborhood.
• The scummiest part of town had the highest crime rates.
• She called him the scummiest person she’d ever met.
• The scummiest layer of foam floated on top of the old soup.