This is the 2370th most frequent Swedish word.
fan
"Fan" in Swedish is a swear word meaning "devil" or used as an expletive like "damn."
In this sentence, 'fan' is used as a colloquial term to refer to someone in a mildly negative tone, often without extreme seriousness.
Vilken fan tog min bok?
Which jerk took my book?
Here, 'fan' is used as an exclamation of frustration or annoyance, commonly used orally in informal contexts.
Fan, jag glömde nycklarna hemma.
Damn, I left my keys at home.
In this context, 'fan' is used as an intensifier to emphasize the irrelevance of something, providing a casual tone to the expression.