Dog-tongues don't take relationships seriously. They like to lead (usually) older and wealthy men on for their own ends before dumping them and moving on to the next victim. Dog-tongues are predatory, using their superficial good looks to snare men and drag them from their existing partners, often with heartbreaking results. A dog-tongue can be compared to the mythical siren.
"Look at her! She's a real dog-tongue!"
"Saturday night - the dog-tongues are out again"