A modern version of a pre-19th century expression: "Sir, you have come over all
unnecessary!"
The above phrase meant that a male was either becoming flirtatious, or causing a female to become very attracted to them.
An 'Unnecessary Man' is a male who can be
associated with this era by looking dashing or wearing an
appropriate costume, causing women to be attracted to them. It is usually applied to characters in books or films, and the look is often twinned with a bad or aggressive attitude.