A brawl that erupted between dozens of people onboard a cruise ship was caused by jealousy over a threesome between passengers, according to a witness. A travel agent who was witness to the fracas told Fox News that the punch-up began over allegations of cheating - in particular, an alleged threesome which then upset the participants' respective partners. Video of the fracas depicted a chaotic scene as between 40 and 60 passengers began punching and shoving one another.