"Flarfing" refers to the act of slurping out the contents of another's anal cavity, after it has been ejaculated and vomited into by some person(s).
A related subcategory, "flarfblasting" consists in expelling by means of flatulence the vomit and ejaculate contents of one's anus into the mouth of another (who could or could not be the person who deposited those contents), positioned directly behind the anus.
When a play fight with a guy or girl turns into sexual actions or sexual intercourse.
John: "Becky you know me and Jasmine were Flarffing last night?"
Becky: "For real? I didn't think that would happen between you guys!"
John: "Yep....it did! I Flarffed the fuck out of her!"