What does “Sunshine,” when it’s placed at the end of sentence mean?

I came across a peculiar (to me) usage of the word, “sunshine” that was placed at the end of sentence in the short story, “High Heels,” written by Jeffrey Archer.

“Sunshine” appears in the following exchange of words at the last scene where the shoes trading company owner, Des Lomax who seemingly set fire to his building and Alan Penfold, training actuary of the fire insurance company who suspects him as the arsonist confront for showdown:

“I will be recommending that my client settles for two million, but it will be up to you to make the final decision, sunshine,” said Alan.

“I don’t give a damn about your recommendation, sunshine.” said Lomax.

What does “sunshine” mean in the above context? Is it an addressing word or interjection? Is “Sunshine” casually used in this way in both British and American English, or is it peculiar to British English? And, what is the origin of this usage?

Solution 1:

In this case, "sunshine" is a fairly condescending term of reference for the other person. This slang dictionary writes:

form of address for a person, usually female.

As this forum adds, calling someone sunshine is usually part of giving a threat. This is the context in which your examples use it--each man is threatening the other, so they are referring to each other as "sunshine".

It is difficult to find exact origins for many slang terms, but one possibility is that it is simply a term of endearment being applied sarcastically. This appears with other words, such as "princess".

You can use sunshine as a nickname for people in a positive sense, too. It can often mean that a person is always smiling and happy, warm like a ray of sun.

It can also be used fairly sarcastically, to mean someone who isn't warm and happy. For example, if you wake someone up in the morning and they're grumpy, you could say:

Good morning, Sunshine!

Solution 2:

The characters are being sardonic, so sunshine becomes a disparaging statement. It is also a term of endearment. Under normal circumstances, if you refer to someone as 'sunshine', then that person is special to you. This expression also gains added currency in places like England, where the weather is usually cold, grey and generally, 'bereft of sun'.

Solution 3:

In Australia, we (as in myself and others I know and have known in the past - in particular, one of my high school teachers) use it as a condescending way of saying 'mate'. Though the older folk may use it as a term of endearment. But personally, amongst friends, we sometimes call each other "sunshine" pronounced with a bit of a twang for the full effect.

The connotation of the word depends on the speaker's tone. So "Good morning, sunshine." could have two different meanings.