This seedy, noir-drenched, serial-homicide case involves the puppet cast of a beloved ’80s children’s TV show who are being murdered, one-by-one, prompting a disgraced LAPD detective-turned-private detective puppet to investigate.

Phil Phillips (voiced by Muppet vet Bill Barretta) is hired by femme fatale Sandra White (Dorien Davies) to stop the killings, which he’s eager to do, since one of the stars was Phil’s brother Larry (Victor Yerrid) and the show’s only human actress, Jenny (Elizabeth Banks), was once Phil’s lover.

Complicating matters is Phil’s troubled relationship with his former LAPD partner, Detective Connie Edwards (Melissa MCarthy), who — after being seriously injured during the incident that destroyed Phil’s career — underwent emergency abdominal surgery in which she received a puppet liver. As a result, Connie has developed a serious sugar addiction, prompting her to gulp huge quantities of maple syrup.

The trademark lawsuit prompted by the film’s release is — by far — its most interesting aspect. The highly reputable Sesame Workshop sued STX Entertainment’s “deliberate effort to appropriate its SESAME STREET mark, and its trusted brand and goodwill, to promote their R-rated movie.”

While Sesame Street objected to STX’s bawdy use of explicit, profane, drug-using, misogynistic, violent, copulating, and even ejaculating puppets, along with the tagline “NO SESAME, ALL STREET,” Judge Vernon Broderick turned down their plea, deciding that tagline distinguished this film from Sesame Street in “a humorous, pithy way.”

Written by Todd Berger and directed by Muppets creator Jim Henson’s son Brian Hanson, it’s simply not funny except, perhaps, when it focuses on comedienne Maya Rudolph, as Phil’s secretary, who’s secretly in love with him.

Instead, the most interesting aspect is the lengthy, end-credit blooper reel showing how the green-clad puppeteers are digitally erased in order to seamlessly integrate puppets with humans — doing porn.

On the Granger Movie Gauge of 1 to 10, “The Happytime Murders” is a crude, trashy 3. Stale vulgarity.