Firing a rather tepid opening salvo in Hollywood’s annual Valentine’s Day rom-com blitz is When in Rome, starring Kristen Bell (Forgetting Sarah Marshall, TV’s Veronica Mars) and Josh Duhamel (Turistas, the Transformers flicks) and directed by Mark Steven Johnson (Ghost Rider, Daredevil). You read that correctly: Johnson, a guy who gave us two critically-reviled comic book flicks, was tapped by Disney to direct a movie entirely devoid of acrobatic fight sequences or computerized visual effects, the only filmmaking skills for which he’s received consistent praise. Hmmm ... maybe this is why Dick Cook was fired.

　　 Bell plays Beth, a high-strung New York City museum curator whose frustration over her barren love life spills over at her sister’s wedding in Rome, where she winds up drunkenly splashing around in the city’s fictional “Fontana D’Amore.” The embarrassing but harmless episode takes a momentous turn, however, when Beth absentmindedly steals a handful of coins from the fountain, unknowingly triggering an ancient Italian curse. Soon she’s romantically besieged by a diverse and highly aggressive group of oddballs played by Danny DeVito, Dax Shepard, Will Arnett and Jon Heder — the very men whose coins she plucked from the fabled fountain.

　　 The concept isn’t entirely without potential, but When in Rome’s script takes the quartet of previously funny actors and comedically castrates them, forcing them to survive this creative Dust Bowl on precisely one joke apiece. DeVito, playing a sausage magnate, emits only meat-related quips; Shepard’s self-obsessed model explores the comic possibilities of his washboard stomach; hapless street artist Arnett plasters the city with nude portraits of his unrequited love; and Heder’s wannabe magician mounts a series of botched magic tricks. (In a gag that might have been funny back in 2004, Efren Ramirez, Napoleon Dynamite’s Pedro, enjoys a cameo as Heder’s videographer. He’s this week’s winner of the Jeff Zucker “How Does This Guy Have a Job?” Award.)

　　 All of which serves to delay the inevitable coupling of Bell and Duhamel, two likable leads who gamely trudge through material so inane, so bland — and so safe — that it could fit comfortably in one of Dwayne “The Rock” Johnson’s increasingly soporific family comedies. In fact, I’m not even sure if When in Rome made use of the standard PG-13 allotment of one F-word (used in a non-sexual manner, of course). Expect to hear it used liberally, however, by fellow audience members as the credits roll on this middling debacle.