Christopher Bird’s review published on Letterboxd :
Mae Whitman and Robbie Amell have superb chemistry together, and that's nice, and they're both good actors as a general rule too. That helps you get through most of this movie, which is... not great.
It's not great on multiple levels. There are the jokes, most of which feel like the product of a forty-year-old man trying to write teenagers. (There is a big comedic setpiece wherein people discuss unfriending one another on social media, and you know it was supposed to be one of the big gags in the movie because it gets so much emphasis, and it's absolutely terrible: it's written by someone who thinks social media is stupid, and therefore that the characters are stupid for caring about it. You can't write a good scene when you think your characters are dumb.) There is the same "OMG high school is all a bunch of cliques" social observance that has been the model for every teen film since THE BREAKFAST CLUB and which is never smart or incisive; at this point it's actively lazy.
And, of course, there is the work they put in to try to make Mae Whitman - who is actively adorable and sexy - into the titular "designated ugly fat friend." It's the exact same shade of stupid that was on display in THE TRUTH ABOUT CATS AND DOGS, except that movie at least tried to justify it by employing a misdirection plot. This one just takes it straight, and it's ludicrous, all of the time.
I did like that all of the cast and crew in the credits got to list their Twitter handles, though. That was clever.