Despite almost universally bad reviews, “Couples Retreat,” the new romantic comedy staring Vince Vaughn and Jon Favreau, directed by their pal Peter Billingsley, was the number-one movie at the box office this weekend, earning about $35 million.

True, there wasn’t much competition–”Zombieland” and “Whip it’ had moved to an earlier week, and the phenomenon called “Paranormal Activity” is still only playing in a few towns–but the healthy haul does represent Vaughn’s best opening since “The Break-Up” in ‘06. And it seems to vindicate whoever decided to soften the movie to a PG-13 rating by removing a subplot in which Favreau cheats on wife Kristin Davis. That subplot was even referenced in an early trailer for the film.

Favreau reportedly was called back from the set of “Iron-Man 2,” which he is directing, to reshoot some scenes for “Couple Retreat” and make his character more palatable.

There’s an old maxim in Hollywood that women won’t go see a comedy in which a man cheats on his wife. So the focus-group mentality prevailed.

Which reminds me of another old maxim: Nobody ever went broke underestimating the intelligence of the American public.