Her speech at his wedding
This is, in my opinion, the best scene in the movie. I thought Lily Collins was great in this movie and this scene in particular.
Her speech was simple and eloquent, and I could sense the years of unexpressed feelings behind her words. She summed up what she felt about him for probably her entire life. That took a ton of courage to bare her soul to him, and during her wedding toast no less.
I think most can relate to having that one person in your life that you just couldn't quite work things out with, but you knew was somebody special. What she said about life being grey if you're with the wrong person but Alex making everything Technicolor..wow. I've always fantasized about making a speech like Rosie's. Just laying it all out there, the truth for all to see. I'll have my chance, some day. :)