Ben Stiller has made a lot of junk over the past few years, and Tropic Thunder feels like an attempt to cleanse these projects from his system. This is a merciless Hollywood satire, in which the crappy movies that Hollywood produces and the narcissistic stars the system nurtures come under fire. Helping lampoon everything from pompous war films to Oscar-baiting stars to Eddie Murphy’s Klumps franchise is a hysterical cast that includes writer-director Stiller, Robert Downey Jr., Jack Black and Tom Cruise.