About 4-14% of people have a genetic variation in the OR6A2 gene, which makes cilantro taste like soap to them. This gene is associated with sensitivity to aldehydes, which are chemicals found in cilantro as well as in soap, giving it that unpleasant flavor.
It's so interesting how genetics can influence something as simple as taste! Makes sense why cilantro is such a love-it-or-hate-it herb for so many people.