Argthtjtr

People often use sans, the French word for ‘without’ in English.

What I don’t get, is when should that switch be made. When should I say sans when I really want to say without. Are there any general rules regarding usage, or is it kind of a person-to-person basis/feeling of flowerness.

The Oxford English Dictionary lists the word as:

Now arch. (chiefly with reminiscence of Shakespeare), jocular, and Heraldry.
_{Before the time of Shakespeare used almost exclusively with nouns adopted from Old French, in collocations already formed in that language, as sans delay, sans doubt, sans fable, sans pity, sans return. Even in some of our earliest examples, however, a native English synonym has been substituted for the Romanic n. in the phrase, as in sans biding = sans delay.}

(You can see plenty of examples of it being paired with French expressions in the Middle English Dictionary. However, it's not really used like this anymore.)

Shakespeare used it in some memorable lines:

Bero.

My loue to thee is sound, sance cracke or flaw.
Rosa.
Sans, sans, I pray you.
_{Loues labors lost}

It's also used repetitively at the end of the especially famous "all the world's a stage" quote:

Last Scene of all,

That ends this strange euentfull historie,

Is second childishnesse, and meere obliuion,

Sans teeth, sans eyes, sans taste, sans euery thing.

Once again, let poetry lead you to an answer.

A very well-known usage of sans appears in Shakespeare’s As You Like It, Act II, Scene VII: All the world’s a stage.

The lines describe the stages of a man’s life, and famously ends with the following:

Last scene of all,
That ends this strange eventful history,
Is second childishness and mere oblivion,
Sans teeth, sans eyes, sans taste, sans everything.

When you use sans in modern English, you are alluding to this work, either directly, or via some other writer that alluded to it earlier and perhaps more consciously.

Note the mood that it evokes: the lack of teeth etc. is the consequence of a fully-lived life. There can be self-awareness of the lacking, and a kind of wry humor. We are powerless to determine our lives, but we can find laughter in our responses, absurd though they may be.

So you can use sans in humorous writing aimed at an intelligent and well-read audience.

However, wry humor is something of an art, as these examples show.