In France, we designate by "Bonaldi effect" a particular case of the Murphy's law which states that:
Any demonstration of any product that worked perfectly at the rehearsals will fail miserably during the public demonstration.
It takes its name from Jérôme Bonaldi, a television host who encountered many problems when he presented unusual objects and inventions.
How would you describe such a syndrome in English?
Urban dictionary suggests an appropriate term: demo effect.
Its downside term is that is typically connected with high-tech, and it has other meanings.
From another source:
Similar to [the bonaldi effect], the demo effect: an object, software, etc., used daily with no incident, would present a dysfunction during a demonstration, especially in public. exemple [sic] : bill gates' presentations of different windows, ending with a famous error on a blue screen.
