For whatever reason, "Sesame Street" decided to do all it could to help promote Henson's directing effort by suing, unsuccessfully, over the movie's tag line "No Sesame. All Street." That promotional blip, frankly, might be the most interesting footnote to this muddled exercise, other than the amusing couple of minutes during the closing credits demonstrating the sleight of hand that went into seamlessly incorporating puppets into the human world.Other that, "Happytime Murders" can't tickle the funny bone enough to get more than a few laughs even from Elmo. It's hard to overemphasize the extent to which the puerile humor yields diminishing returns, as the filmmakers (Henson and writer Todd Berger) hammer away at dirty-puppet jokes to the point of wearing holes in them.The basic plot is modeled after an old Raymond Chandler mystery of the 1940s, with hard-bitten detective Phil Phillips (voiced by Bill Barretta) having once been the only puppet to ever serve on the police force. A perceived lapse got him ousted, forcing him to seek work as a private eye on behalf of puppets, who are the one group it's completely tolerable to discriminate against in the City of Angels."It's their world, and we just live in it," Phil says grimly near the outset.The combination of a murder and a new client, however, puts Phil on a murderer's trail, trying to figure out who's killing off performers who were once part of a kids TV show titled "The Happytime Gang." Since Phil has a connection to the program, let's just say this time, it's personal.Phil's sleuthing, and the growing pile of unwoven and otherwise shredded puppet bodies, brings Phil back into contact with his old partner, Det. Connie Edwards, played with reckless abandon by Melissa McCarthy, who does her best — for a while, anyway — to prove she can out-cartoon the puppets.Alas, the novelty (as well as the wit and energy) rapidly wears off, leaving in its wake a lot of blunt language and a few fitfully inspired sight gags — the best involving a puppet sexual encounter, which drags on (and on) much like a gag in another crude-puppet movie, "Team America: World Police."In addition to McCarthy, Joel McHale, Maya Rudolph and Elizabeth Banks are part of the non-puppet contingent, but everyone is fighting against the same downhill drag, counting on the pitch "R-rated puppets" to do practically all of the heavy lifting.Having directed a couple of Muppets movies in the 1990s, Henson told USA Today that his dad — who produced more adult sketches for "Saturday Night Live" — would have embraced what he's done with "Happytime Murders," which sounds only partly accurate.The late Henson — a genius and visionary — certainly played to adults as well as kids, and would likely have welcomed the idea of stretching puppets into new dimensions. It's the execution that he — and frankly, practically anyone else that doesn't have cotton stuffed between his or her ears — would be hard-pressed to love."The Happytime Murders" premieres Aug. 24 in the U.S. It's (gleefully) rated R.