Sneak previews are sometimes a treat for reviewers, who are used to seeing movies with grumpy, chatty colleagues or on DVD: it can be good to be a civilian, among grumpy, chatty moviegoers who decided to catch a movie a week early. Sneak preview audiences are what’s sometimes called “self-selecting”: they’re the people who really want to see a movie based on its trailer or its stars or some form of buzz, tangible-or-not. I’m vamping around the subject of David Schwimmer’s feature directorial debut, “Run, Fat Boy, Run,” which is what years of dreams and great fortune has led the “Friends” actor toward. It is to cry. The bits of “Friends” I’ve had the misfortune to glimpse over the decades are as cringemaking to my taste as anything I can recall in comedy: Schwimmer’s relentlessly unpleasant persona makes Ben Stiller seem the most comfortable creature in the Hollywood bestiary. But his star here is the affable, game Simon Pegg, star and co-writer of “Shaun of the Dead” and “Hot Fuzz.” But Schwimmer, in telling the tale of Dennis, a dismal London basement-dweller who dumped pregnant fiancée Libby (Thandie Newton) at the altar five years earlier, shows few skills worth bragging on. Hank Azaria, a gifted voice artist who often chafes when visible, plays Whit, Libby’s new beau, a runner, which challenges “fat boy” lingerie shop security guard Dennis to get into shape. Uninspired underdog routines ensue. Weak tea from the get-go, “Run, Fat Boy, Run” is a big nothing. I failed to spy a single smiling face on the way out of the theater. It was Saturday night, and visions of drinks seemed to dance in the air. 95m. (Ray Pride)