Complex sentence: Taboo terms are used as insults, epithets, and expletives because they damage the listener's face, which might destroy social harmony--especially if the speaker and listener are socially distant from one another.
Split into simpler sentences: Taboo terms are used as insults, epithets, and expletives because they damage the listener's face which destroys social harmony. This is the case especially when the speaker and listener are socially distant from one another.