Latest one which I am going to start using for big games on a regular basis is to ensure my 13 year old daughter leaves the house in a stinking bad mood.
Happened twice so far - Dons 2 Celtic 1 (Quinn 90th minute winner) and Dons 2 The Rangers 1 (thanks Maddison).
Only problem is the length of the journey to the semi-final - don't fancy putting up with her on the train (easier to ignore the mood when walking)