It varies depending on region, culture, and generations. My relatives rarely swear, but my author colleagues from New York use the F-word casually and routinely. And I once overheard a conversation by two younger men on a bus in which a certain four-syllable epithet was used in pretty much every sentence, essentially as a pronoun, and was so casual and stripped of meaning that it had become elided to "m'fuh" or "m'fug." And yet when one of the speakers wanted to convey genuine offense, he said, "What the hell?!