In the context, KISS is in no way scatological or obscene. It may be offensive only to the poor recipient of the advice being told his work is over elaborate.
It is widely used in the engineering world, and is a useful maxim for everyone trying to communicate. It is often used when a complicated solution has been found to a problem, and the resulting thing or process maybe exceeds the constraints available.
Surely, in the example
On the possibility of producing a greetings card that displays the text of an original poem
is unnecessarily verbose, and the essence of the title is contained in the suggested
Include a poem in a greetings card.
with no diminution of meaning except the unnecessary "original."
It has limited application in the literary world, where style is significant.
BTW I believe it means Keep It Simple Stupid, not the other way round.