One star, Rated PG-13, 110 minutes “I Feel Pretty” suffers from a fatal flaw: its premise. Built around the notion that there’s something inherently hilarious — even crazy — about a woman not supermodel-thin or -gorgeous behaving with the confidence of one who is, the comedy treats its star, Amy Schumer, as if she were Chris Farley in the “Saturday Night Live” skit “Chippendales Audition.” In that classic sketch from 1990, the late actor — nearly 300 sloppy pounds of him — does a sexy striptease next to a nervous, insecure and very buff Patrick Swayze.