An abbreviation for "Flirty Fishing", a tactic used by the Children of God cult (also known as The Family
International, Teens for Christ, COG, The Family of Love and The Family) would use to recruit new members by sending female acolytes to bars and other establishments of ill repute to have
sex with men in order to convert them to
Christianity. The term "ffing" became widely used when members became aware people knew what "flirty fishing" was, and therefore needed to be more coy and obfuscate the name of the tactic their cult was based around.