The phrase 'Son of a Gun' is used to describe a despicable or worthless person, usually male. The term can also be used as an exclamation that indicates surprise. It is sometimes used to compliment or encourage.
Example of Use: "That son of a gun tried to steal my car from my driveway!”
The phrase 'son of a gun' originated in the British Royal Navy during the 1800s, when Naval officers were allowed to have their wives accompany them to sea, and babies born aboard ship were delivered in the spaces between the broadside guns. The term applied to boys born at sea and was slightly contemptuous.