What is the origin of the idiom "French leave" and when to use it?

The idiom "French leave" is believed to have emerged in the 18th or 19th century and is associated with British usage. The term "French leave" does not have a direct connection to French culture or practices. Instead, it is thought to have been a playful or sarcastic way for the British to describe an unannounced and unauthorized absence, suggesting that the French were known for their nonchalant or carefree approach to such matters. It's important to note that the term may carry stereotypes or outdated connotations, and its usage should be considered with sensitivity in modern contexts.