Geek Press points to 20 things that only happen in movies, but the list isn't that great. I'm sure I can come up with better ones. (And if I don't, I can just delete my attempt before posting it.)
1. Any computer system can be hacked in 60 seconds.
2a. Phones always ring during a break in conversation...
2b. ... and the call is always relevant to the scene...
2c. ... and there's no call-waiting.
3. No one ever thinks of a better come-back to an insult the next day.
4. If you meet someone and arrange to go on a date, you'll offer to pick them up tomorrow at 8 but never exchange addresses or phone numbers.
5. Rogues are always lovable and endearing.
6a. All combat is eventually resolved hand-to-hand.
6b. The bad guys attack one at a time.
6c. Small, fast people can beat up large, strong people.
6d. When you punch or kick someone, they go flying across the room.
7. Stalking a woman makes her fall in love with you.
8. The dumbest, most annoying, most bumbling character will be a white male.
9. Breaking the rules always turns out well.
10. Anyone can jump a 10 foot chainlink fence with minimal effort (unless a dog is in pursuit).
11a. Getting thrown through a window is merely a minor annoyance.
11b. Likewise falling down stairs.
12. All offices have windows.
13. 95% of computers are Macs.
14. Cars are always clean, even if they're old and busted.
15. Pedestrians are never hit during a car chase.
16. Getting shot once anywhere by any gun will knock you down.
17a. Old people are amazed and confused by the antics of young people.
17b. White people are amazed and confused by the antics of black people.
18a. Caves and tunnels will never be pitch black, but will always be lit by concealed, indirect lighting.
18b. If you turn off the lights in a room at night, lights outside a window will turn on.
19a. It's easy to chop off a head or limb with one blow...
19b. ... and to cut through armor...
19c. ... and to jump onto a horse while wearing armor...
19d. ... and to run around in armor.
20. Animals are invulnerable.
21a. Kids are smarter than adults.
21b. Kids can drive cars.
21c. Kids can beat up adults using karate.
21d. Kids are always good judges of character.
22a. High school students are 25 years old...
22b. ... and still wear their backpacks on one shoulder.
23. Only bad guys smoke (these days).
24. Ugly people are just beautiful people with dumpy clothes and bad haircuts.
Not that these are all new or original....