Related Clues:

• Act the fink
• Scoun-drel
• 'You dirty --!'
• Stool pigeon
• One who sings
• Wharf pest
• Sewer resident
• Common test subject
• Muppet Rizzo, e.g.
• Plague carrier
• Dirty dog
• Nocturnal rodent
• Untrustworthy one
• Untrustworthy sort
• It may be down in the dumps