Fan!
A swedish word meaning "fuck!" In english and even an old swedish name for satan.
You lose in a game and screams:
-Fan!

(pronounced as FAAANN!)

You mess something up and your mom says:
-vad fan är det här!?!?

Meaning "what the hell is this!?!?"

(in this case you can choose hov many a's you want in order how angry or sad you or you mom/dad or friend are.