Adam Devine and Zac Efron play the Mike and Dave of the film's title, respectively, two irresponsibly party animals who've merely used all their family get-togethers as excuses to get drunk, chase skirts, and invariably embarrass their kin through shenanigans that cause more mayhem than mirth (the Wedding Crashers comparisons are so obvious they're practically obvious to reference it during the movie). As such, when it comes time for their sister Jeanie's wedding in Hawaii, the family makes it an absolute requirement for them to bring dates along to, hopefully, keep their ids in check. They can't just bring any dates though, they must be “nice girls” that meet the approval of their sister and parents. Not really knowing any nice girls personally, Mike and Dave take to the internet to advertise an all-expenses paid trip to Hawaii for women who would fit the criteria of not only being respectable enough for the family to give their blessing to, but also attractive enough for the young men to get it in the sack before the excursion is complete. After an extensive round of preliminary dates (the ad, understandably, goes viral), the boys settle on Tatiana and Alice, who pretend to be good girls in order to score the vacation, but secretly are even more irresponsible hedonists than Mike and Dave.