It's a bit like Cluedo except in reverse. Instead of guessing "Mr Plum in the library with the candlestick." you get a scene from a movie and need to name that movie. Don't read the other comments until you've posted your answers (assuming you want to).
Some of these should be easy, and some of them I imagine won't be.
ETA: Updated with where the scenes were from, and whether they were guessed correctly or not.
1. Hugh Grant killing us, not so softly, with his song. (About a Boy) Yes
2. Bigfoot dancing to the Bee Gees. (A Goofy Movie) No
3. A young girl falling down flights of stairs, smacking straight into a wall, and it being one of the few moments of humour in the film. (Spirited Away) No *this surprised me*
4. Taking out the garbage was never meant to be extremely sexy. But it is. (Batman Begins) Yes
5. What better way to tell your son you love him than teaching him out to shoot things dead? (Flower & Garnet) No
6. An aged 'boy' and a man with a huge head dance together. Wonderfully. (Sky High) No *Yeah, I really didn't expect anyone else to get this one, but Dave & Kevin are One True Platonic Pairing omfg*
7. Beavers, beavers, everywhere, but especially on the road. (Men with Brooms) Yes
8. Nick Cave appears to be turning into a literary figure. No, sorry, that was Tom Waits. Nick Cave. Tom Waits. Nick Cave. Both. (Shrek 2) No
9. I didn't know aliens could play guitar, nor that they'd want to wear white jumpsuits when doing so. (Lilo and Stitch) Yes
10. A cafeteria is set out like this, as funky music which sounds like the Futurama theme tune plays. (Mean Girls) No
11. Touch my stump. (Hard Core Logo) Yes
12. Alfred Molina is very sorry, he couldn't help himself, yes he knows he's ruined the display. (Chocolat) Yes
13. Don't stop me now, I'm having such a good time - demolishing this zombie. (Shaun of the Dead) No *again, very surprised no-one got this*
14. Jack-in-the-boxes are too scary, especially when Jazz is playing in the background. (Harry Potter and the Prisoner of Azkaban) No *umm, hello, people? most of you claim to be HP fans*
15. Lara Flynn Boyle knows that nothing says "I love you" like your crazy stalker falling through a glass ceiling. (Wayne's World) Yes