Fun is what happens when you are doing something and are enjoying it.
These things are fun:
- killing a Sue
- playing in the All-HQ Australian Indoor-Rules Quiddich League
- Getting completely drunk and singing karaoke
These things are not fun:
- going through the mission so as to get to the Sue.
- losing to the DBS team at Australian Indoor-Rules Quiddich (because they firmly endorse the down-trou rule).
- Finding out your partner recorded you taking a go at karaoke.
"Fun" is also the recorded official word of Agent Acacia Byrd of the Department of Mary Sues, the famed Assassin who is now, sadly, retired.