“A bad penny always turns up” is often spoken about bad people who appear when they are unwelcomed. It is used in a deprecating manner for a person or thing that turns up at an inopportune time, or when the time is not suitable or appropriate.
The origin of “a bad penny always turns up” is stated to have emerged in or around 18th century but exact usage is unknown. However, Morris Dictionary of Word and Phrase Origins put it as used by Sir Walter Scott in as “Bring back Darsie? Little doubt of that. The bad shilling is sure enough to come back again.”
Examples in Sentences:
Example #1: It is used as a metaphor such as “He is a bad penny and will always turn up.”
Example #2: Trump is a bad penny and he always turns up when he needs the least.
Example #3: It can be used as a simile as “Most unwanted people are like bad pennies and they turn up when they are not needed.”