Going into the summer, Baywatch seemed like a surefire hit. It had two huge stars in Dwayne Johnson and Zac Efron, a great supporting cast, and a director who knows how to sell big-budget comedies. But the film did a massive belly-flop at the box office over its opening weekend, falling way short of expectations, earning just $18 million in the US. So what went wrong with Baywatch? Here are some of the reasons the movie bombed.