A love-at-first-sight meeting between Nancy and Robert justifies a quick wedding that brings the four together as a family under the same roof. This forces the two adult children to share a room, and they deal with it about as well as real 12-year-olds would; a nasty step-sibling rivalry where sacred toys must not be touched, dinner table stare-downs are law, and vicious insults and threats are all in a day's work.

Basically, two brand new siblings acutely distressed and anything but ready to engage in brotherly love. They spend the first part of the movie hating each other, with ongoing injurious pranks that include a set of (prosthetic) balls getting rubbed on a drum set and a dramatic battle in the front yard, in which a shovel and a bicycle are both used as weapons.

Eventually Dale and Brennan bond over their mutual hatred of Brennan's brother, Derek (Adam Scott), a rich egotist bully whose cruelty as a teenager thoroughly traumatized his brother.

Step Brothers is essentially a throwaway film, one that might have gone straight-to-video if Apatow had not had such a hot hand. It's not that any of this stuff is offensive, it's just hackneyed and flat.