If you’re not familiar with the sexual, er, technique after which "Donkey Punch" is named, we’d like to direct you to Urban Dictionary. Go ahead, we’ll wait.

One could pretty easily make the case that no one’s actually ever performed a donkey punch, that it’s merely the substance from which apocryphal bar stories are formed. But a character is goaded into giving it a try in music video director-turned-first-time filmmaker Olly Blackburn’s gratifyingly nasty midnight movie, with grotesque results. At the film’s outset, three British girls on a weekend holiday in Mallorca meet three good-looking young men in a bar by the beach. The boys have been crewing a yacht for an owner who’s not around, and soon they’ve persuaded the girls to join up with another of their friends on the boat in the open water for drinking, drugs, sex and eventual horrific violence. Things escalate, "Very Bad Things"-style, out of seemingly rational urges toward self-preservation that go disruptively wrong, with the added jolt of psychological needling between both sets of supposed friends. The girls in particular don’t immediately grasp that the boys, who are spending a few months slumming in more pleasant climes and dappling in thoughtless hedonism before heading back for law school or careers in the military, have ambitious futures they’re willing to go to great lengths to protect. But in the end what makes "Donkey Punch" work so well is its simply believable depiction of how quickly situations can turn. "Can you believe that yesterday we was in Leeds in the sodding rain?" shrieks one of the girls happily as they dart from bar to bar in the honey-golden Spanish sunlight. Give it another twelve hours, and you might find yourself curled up in a yacht in international waters, hoping a scrounged kitchen knife will be enough to defend yourself.

"Donkey Punch" currently has no U.S. distribution.

+ "Donkey Punch" (Sundance)