It's a derogatory and offensive phrase, typically used in a humorous or mocking way.
Here's why it's considered offensive:
* "Dusty" implies someone is old, outdated, or has been neglected.
* "Muffin" is a term used to describe someone who is overweight or unattractive.
The combination of these words paints a negative picture of the person being described.
It's important to remember that using this phrase is disrespectful and can hurt someone's feelings. Instead of using this slang, consider using respectful and kind language.