You just have to be impressed by Jenson Button. Many drivers on the
current F1 starting grid, faced with the consequences of a rare McLaren
cock-up prior to the warm-up lap at Monte Carlo, would have been tipped
right over the edge and completely lost their cool (yes, I’ve just seen
the inadvertent joke too!).

Leaving a ‘cooling cover’ in a radiator
duct was a significant error and by the time the error had been realised
the Merc V8’s temperatures had soared to an irretrievable level.

The cooling cover is a simple foam bung designed to seal the sidepod in the garage to prevent airflow through the sidepod and maintain engine temperature after engine warm-up.

 This bung was not removed before Jenson's car drove to the grid and would have prevented any air flowing though the sidepod, radiator and top body.Damage from overheating components under the top body ultimately caused the car retirement.

Rather than fire off  ‘what a bloody shower, wasting my time like this’ which would have been as intemperate as it is inaccurate, Jenson just shrugged in a ‘just-one-of-those-things’ fashion and admitted at the end of the race (in which he took no part) that he’d forgotten it already.