fornicating
Fornicating (verb) means present participle of "fornicate" — having sexual intercourse, typically outside marriage; also used loosely and crudely as a generic intensifier in place of a stronger swear word.
How to use fornicating
Learner’s notesIn plain EnglishHaving sex outside marriage; in slang, sometimes just a crude filler word rather than a literal reference to sex.
The literal sense is formal/old-fashioned or legal/religious in tone; the intensifier use is vulgar slang.