Mark Ruffalo and Jennifer Garner in 13 Going on 3013 GOING ON 30

When you watch a body-switching comedy such as Big or Freaky Friday, you know immediately that the movie is going to require a huge suspension of disbelief; these are comedy fantasies, after all, and bitching about logic and realistic plotting is the surest way to kill your good time.

Nia Vardalos and Lainie Kazan in My Big Fat Greek WeddingMY BIG FAT GREEK WEDDING

In the first 20 minutes of the romantic comedy My Big Fat Greek Wedding, there's a scene so simple it feels revelatory. Our heroine, Toula (Nia Vardalos), is a 30-year-old waitress in a diner owned by her Greek-with-a-vengeance parents, and has always been, as she describes herself, "a frump" - plain, bespectacled, overweight, and sadly single.