Colorful metaphor or profanity is a use of language or physical expression intended to emphasize derision, curses, or other emotional outbursts. Although such usages were uncommon in the 23rd and 24th centuries, they were an essential part of 20th century conversation, seen in the novels of "giants" such as Jacqueline Susann and Harold Robbins.
In 2155, ambassadors at the meeting to form the Coalition of Planets noted that xenophobic Humans were using "language that is not programmed into the universal translator", which Nathan Samuels brushed off as emotional outbursts during a stressful time. (ENT: "Terra Prime")
When the crew of the USS Enterprise time traveled to 1986, James T. Kirk began using "colorful metaphors" in an effort to blend in. However, he felt that Spock shouldn't attempt them, as he didn't "have the knack." (Star Trek IV: The Voyage Home)
William T. Riker commented that Alidar Jarok's knowledge of Klingon curses was impressive, after Jarok had referred to Worf as a tohzah, adding that "only a Veruul would use such language in public." (TNG: "The Defector")
Klingon Governor Vagh, swore to Picard after Picard denied the charges of supplying weapons to terrorists. Picard returned the favor. (TNG: "The Mind's Eye")
When the USS Enterprise-D was about to crash into Veridian III, Data expressed the shock and horror he felt (thanks to his newly installed emotion chip) with a suitably colorful metaphor, saying "Oh shit." (Star Trek Generations)
The Species 8472 recreation of Boothby, stationed on Terrasphere 8, referred to the concepts making up the United Federation of Planets: "tolerance for all species, the Prime Directive" as "targ manure," during talks with Kathryn Janeway and the senior staff of USS Voyager. In response to those statements, Tuvok corrected Boothby and stated "your metaphor is colorful, but inaccurate." (VOY: "In the Flesh")
Miles O'Brien used mild Irish expletives, usually the word "bloody." On one particular occasion, when Molly O'Brien fell into the past through a time portal on the planet Golana, he used the stronger expletive "bollocks" when some of the equipment he used in an attempt to retrive her malfunctioned. (DS9: "Emissary", "Q-Less", "Empok Nor", "Time's Orphan")