Ben Stiller is back in the sendup business, nibbling gently at the soft, manicured hands that feed him and co-stars Robert Downey Jr., Jack Black (wasted here), Matthew McConaughey (doing Matthew McConaughey), and, of course, Tom Cruise in a career-resurrecting role as a bald-headed, big-gutted, foul-mouthed studio boss. Stiller, having long moved on from sitcom social commentary (Reality Bites) and grim irritainment (The Cable Guy), is back doing the affable, well-heeled snark of his short-lived 1992 Fox sketch series, relying on the in-joke that’s been out in the open since Charlie Chaplin was making short films about movie sets in 1916. A bunch of actors (Stiller, Black, Downey) are supposed to be making the archetypal Vietnam War movie based on the memoirs of an aging hero (Nick Nolte). But days into shooting, rookie director Damien Cockburn (Steve Coogan) is already weeks behind, so he drops his cast into the Southeast Asian jungle in order to achieve vérité. Things go awry when Stiller’s Tugg Speedman is taken prisoner by armed thugs farming poppies and life suddenly imitates art, blah blah blah. When it isn’t tossing softballs at the studios, Thunder is the very thing it parodies: a wall of noise engulfed in flame.