With kids heading back to school on Tuesday in many areas of the country, 3 R-rated movies are debuting this weekend -- and none is expected to produce sizable returns at the box office. (The Labor Day weekend is the only major U.S. holiday that does not see a spike in ticket sales; in fact, it generally sees a downturn.) Likely to come out on top -- but not by much -- say forecasters, is Machete , co-directed by Robert Rodriguez and Ethan Maniquis, and boasting a cast that includes Robert De Niro, Steven Seagal, Don Johnson, Jessica Alba, Lindsay Lohan, Cheech Marin, and Danny Trejo as the machete-wielding killer, named Machete. It will be up against the George Clooney thriller, The American, which opened to mixed reviews on Wednesday, and the romcom, Going the Distance , starring Drew Barrymore and Justin Long. Each film is expected to earn in the neighborhood of $15 million.