Bianca (aka "B," played by Mae Whitman) is an honour student with two beautiful (and intelligent) friends. But she throws it all over when hot football star, childhood friend, and neighbour Wesley (Robbie Amell) casually mentions she's "the DUFF," or Designated Ugly Fat Friend. Which leaves her with no support group in high school, not an ideal situation. She asks Wesley for guidance on de-DUFFing herself. This leads to the worst section of the movie as Wesley has her trying on clothes - she strikes idiotic poses in fantastically ugly clothes. And then he has her approaching random men in the mall to "learn how to talk to men." And after all the idiocy in the mid-section of the movie, Bianca suddenly delivers this incredibly calm and perfectly worded monologue to her enemy at the climax of the movie ... one of these characters wasn't her. But in classic movie style, the writer and/or director made her both in the name of humour.
There are some scenes between Whitman and Amell that are very funny, but for the most part the movie finds its humour in humiliating people - and then ultimately claims to be about respect for individuals and their differences.
I have to give credit to Whitman though: my jaw dropped when I found out where I'd seen her before. She was Roxy Richter in "Scott Pilgrim vs. the World," and it's hard to imagine two less similar characters than Roxy and Bianca.