Acronym for Unexpected (or Unintentional) Farting Throughout Intercourse. Used as an interjection, generally interchangeably with "fuck!", but while "fuck!" can be used in any situation from a mild annoyance to a life-shattering catastrophe, the grim image of letting a stream of stinkbombs loose whilst banging the girl of your dreams should be reserved for the latter.
"Great, of course I have a heart attack when I'm hours from the nearest hospital. UFTI!"
"My nose! Now I'll never be a teen model! UFTI!!!"