This is a girl that has up to three major flaws, but is potential sex material regardless. The flaws can be weight, acne, bad teeth etc. The one exception is bad feet, which is unacceptable and is an automatic disqualfier.
She is driving a bucket, but she is a swan all day.
A female who, when younger, was a bit of an ugly duckling but grew up to be good-looking. Unfortunately, they have suppressed a lot of resentment regarding being the ugly duckling that she's actually turned into one of those women who are bitchy and arrogant. Much like real swans who hiss and chase you if you so much as look at them and could break your arm
Dude- Hey, isn't that Kelly? She grew up to be hot.
Fella- Yeah, but since that happened she gained too much confidence and started acting like she's better than everyone. She even upset the geeks last week.
Dude- But she was a geek when we knew her from school. She changed for the worse. Shes a swan for sure
Swan: UUhhhh, im a dickhead
Guy: You are such a swan.
NOTE: Swan might actually say something decent, but it just comes out as "I'm a dickhead" to everyone else.