Until this point, “Triangle” presents itself largely in aspirational mode, poking pinholes in the characters’ rarefied bubble. Consider this could-be coincidence: Roughly midway through Östlund’s diamond-sharp, influencer-skewering satire - a fitting follow-up to 2018 Palme d’Or winner “The Square,” and a deserving choice for this year’s top prize - a black-tie dinner aboard a posh ocean cruise goes sideways, touching off an outrageous sequence in which the disgraced attendees, puking every which way, wind up swimming in their own effluvia.