"Mike and Dave Need Wedding Dates" is so close to working one can taste it. When the film keys into a certain groove, it can be uproarious. These comic highlights are just that, though, interspersed between material that tries too hard, underestimates the audience's intelligence, and ultimately falls flat. Tonally, the picture is erratic, weaving between broad physical humor, sharp-tongued bon mots, and dramatic soul-searching. The screenplay by writing partners Andrew Jay Cohen and Brendan O'Brien (2016's "Neighbors 2: Sorority Rising") is uneven, too often relying upon unctuous, worn-out conventions and dumbed-down plotting. It is first-time feature director Jake Szymanski, however, who appears to be the biggest offender. Just when the film should be settling down to treat the characters with a softer, more humane touch, he chooses to play to the rafters with strained, over-the-top histrionics. It is a shame, because most of the actors are clearly game, out to make something better than what has shown up on the screen.

Mike (Adam DeVine) and Dave Stangle (Zac Efron) are twenty-something screw-ups who, no matter how hard they try (not very), always seem to destroy any important family gathering they attend. With sister Jeanie's (Sugar Lyn Beard) destination wedding approaching, parents Burt (Stephen Root) and Rosie (Stephanie Faracy) ask that they find presentable young ladies to bring to the Hawaii nuptials. Naturally, Mike and Dave turn to Craigslist with this unusual proposal, capturing unanticipated media attention (they are guests on "The Wendy Williams Show") but attracting all the wrong kind of women in the process. Fresh out of jobs and tempted by the allure of a paid island paradise vacation, wild best friends Alice (Anna Kendrick) and Tatiana (Aubrey Plaza) conspire to play the parts of responsible, sweet-natured dream women—Alice as a hedge fund executive, Tatiana as an elementary school teacher. Mike and Dave buy into their charade without question, putting into motion a week in Oahu the four of them—and the entire wedding party—won't soon forget.

"Mike and Dave Need Wedding Dates" has two go-for-broke pistols in the form of Anna Kendrick (2015's "Pitch Perfect 2") and Aubrey Plaza (2014's "Life After Beth"), their quirky, gloriously uninhibited turns as Alice and Tatiana significantly overshadowing male co-leads Zac Efron (2016's "Dirty Grandpa") and Adam DeVine (2015's "The Intern"). While Alice and especially Tatiana are uncouth at best, they somehow are able to retain their charm. They feel like real people, flaws and all, and their personal arcs—Alice with coming to terms over being left at the altar of her own wedding, and Tatiana with insecurities about no longer being needed by her best friend—are calculated yet sincere. As emotionally stunted ne're-do-wells Dave and Mike, Efron and DeVine are less funny than simply obnoxious. Performers who give away they are in on the joke are never as successful as ones who play the comedic material straight, and this is the case here. As peppy, squeaky-voiced, increasingly stressed-out bride-to-be Jeanie, Sugar Lyn Beard (2015's "Aloha") steals a number of scenes, including one involving an unorthodox spa trip and another where she has an unfortunate run-in with an ATV during a "Jurassic Park" locations tour. This latter set-piece is a hilarious, well-timed high point.

Enjoyable enough in its first hour to almost be able to overlook its weaker excesses, "Mike and Dave Need Wedding Dates" loses its way during a third act that threatens to dismantle all good will. The contrivances fly fast and furious, from a disastrous wedding rehearsal dinner to an embarrassing ecstasy trip to a last-ditch effort to pull together a ceremony. A backstage brawl between Mike and Dave while their microphones are still on is interminable. A subplot involving Mike and Dave's lesbian cousin Terry's (Alice Wetterlund) attempts to seduce Tatiana leads to a fairly amusing scene in a sauna, but it goes nowhere thereafter and is forgotten about by the end. Through it all, Anna Kendrick and Aubrey Plaza are joys to watch in their roles; a better version of this movie would excise Mike and Dave and focus solely on their characters' raucous misadventures in Hawaii. If only. Reminding of 2008's "Forgetting Sarah Marshall" and 2011's "Just Go with It" but not as rewarding as either of those films, "Mike and Dave Need Wedding Dates" deserves a smarter script and a more confident directorial hold. Regrettably, long before the end, the laughs have been outnumbered by groans.