Unfortunately, "Step Brothers" can only ride on fumes for so long and like much of Ferrell's work, the script depends on gibberish and expletives to keep things "funny." After the novelty of the set-up is gone (which is quick), the actors are left to stand around and make penis and fart jokes just to segue to the next sequence. I've always had a problem with comedies that overdo on their premise. It becomes a crutch and aggravation. After the first 20 minutes of crash bang boom, I'd had enough.
But "Step Brothers" doesn't just beat the dead horse - it buries it and plants the headstone. Example: after Brennan and Dale become buddy-buddy and royally screw up an evening out with their folks, Richard Jenkins bends Will Ferrell over his leg and spanks him. "I should have done this a long time ago," screams the father. Is this really what we've come to? Grown men getting spanked by other grown men? I don't like to watch kids act like kids, but adults doing the same is trip-to-the-dentist level painful.
Studio executives will continue to stick Ferrell and his brethren in these situational comedies until they stop making money, movies where mouths are referred to as "suck holes," the word "faggot" is used far too casually and when Will Ferrell's character gets an idea he says something nonsensical like "It feels like a bolt of lightning just struck the tip of my penis."