The Diary of a Young Girl: she's so funny, that's what hurts
On The Diary of a Young Girl by Anne Frank
I'd only read parts of it in school and I remembered it as solemn. It isn't. She's sharp and vain and complains about her mother and has crushes and rewrites the same entries because she wants to be a writer. She's a real teenager.
That's what makes it almost unbearable, because you know the date the entries stop and she doesn't. Find the complete edition if you can. The earlier versions cut out a lot of what makes her so alive.