To let one go when suffering from serious windy-pops. A polite way of admitting your bodies emission, without using foul language.
It is not neccessary to wear a hat to be able to exclaim that you have dropped it.
Can also used by a third person as an accusative
"I must apologise to you all, I dropped my hat as the doors closed."
"Did you drop your hat again?" said Roy
"No", said Dave, through the smoke rising from his smouldering trousers.