I doubt taboo words are (always, or necessarily) related to taboo thoughts. It's not taboo to think about fucking, but in many contexts it's taboo to use the word instead of its "milder" alternatives.
PS: It's not accurate but many people still think the world started with: "Found/ Under Carnal Knowledge" or "For Unlawful Carnal Knowledge" which comes back to the idea that the word means more than just the act of procreation.
disport
headaches
mistakes
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Alternatively:
pork
mommy & daddy alone time
the beast with two backs
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The possibilities are overwhelming!
Interestingly, I find that some of the more creative "euphemisms" for sex (pork is a middling example) have more shock value when they show up in conversation... the old standards are simply overused, in spite of our best efforts in child rearing, and don't work anymore in conjuring up sufficiently taboo images. Terse, vivid imagery is much more of a live wire.