Robert Heinlein had some Venusian aliens who had a cultural taboo about being seen while eating. Even when briefly tasting something, the polite thing to do was to turn away from other people to do so. A simple, amusing reflection of human taboos.

But nowhere in science fiction is there a taboo like the modern one about using language that suggests that humans come in male and female, and that these form a breeding pair, and actually that this is the norm for the animal kingdom. Nowhere in science fiction are there Type A and Type B in the character creator, or 'theyglish', or circumlocutions like
>In the beginning, God created a person. And then to give that person a significant other to start a polycule with, God created another person.
What could even be this dumb? Perhaps an alien species with a cultural taboo about distinguishing light from darkness.
>In the beginning, God separated different intensities of shadow - though all remained equal. And God said "let there be BOTH darkness AND light"
where it's a severe faux pas to ask if it shouldn't be "light and darkness". You have to change the order or it's light supremacism, OK?