Oh boy! This is like for all three books, I can't think of ha, ha funny. Most of the 'smiling' moments of the books are just the way she turns a phrase. Another ode to Gary Ross' directing. I guess Haymitch growlin' at Katniss is the only funny, ha ha moments in the first movie.
When 18:00-
Reflection became 18:00-
Cat Adoration 
mockingjay when Katniss delivers the cat to 13.
The first two pages with Buttercup.
When Finnick and Katniss wake Peeta up in their gray-green face ointment. This will never fly in the movie, they can't be looking hideously ugly for much more than a scene. Can they? i'll have to think about if they'll make as ugly as they are in the books.....
Boggs after seeing Finnick only in his underwear and being comically provocative when Gale&Katniss get embarrassed over how handsome it's pointed out that Gale looks in a uniform.
I know it won't be funny initially, but when Katniss gets drunk with Haymitch. Maybe? That might be too fresh on the heels of the news.
-------------------------------------------------------------------------------
Edit: Most of the moments to me are like, 'grinning' moments, like on pg 127 of Mockingjay (*frowns if my book's sized like most are*) when Gale has to kick Katniss under table at the meeting where everyone first sees the Mockingjay footage, when the president asks Katniss a question and Katniss realizes she hasn't been ratted out.
But then a couple of pages later Haymitch threatens to lock what she dubs
the head shackle onto her head. If she finds a way out of that, *silver clip comes out* he'll authorize them to implant inside of her head, so that she can never turn his voice off.
They're already at work on "Catching Fire". WoooooooHOOOOOOOOOOO!