Grammar patrol:  An expletive is an exclamatory word or phrase, like "I'll be durned!", or "Golly!" Some expletives use bad words (like "Oh, sh*t!").  But not all bad words are expletives.  Some are nouns, some are adjectives, etc.  Some words can be used as expletives and ALSO as nouns or adjectives.  The bad word in this sentence, for instance is a subjective noun:  "That is bullsh*t".  Here, the bad word is an adjective: "She was f***ing hilarious."

Better to say "vulgarity" than "expletive", unless it really IS an expletive.

The custom of calling all bad words "expletives", I believe, started when transcriptions of the Nixon tapes (which were full of vulgarities), were published in newspapers, with the vulgarities deleted.  The transcribers kept typing "expletive deleted".