I learned a lot from MW2, how about you?
Note: If its a spoiler place it in a spoiler tag please.
 
1. "You can shoot down UAVs" - Jeff

2. Riot shields will protect you from a direct RPG hit.

3. Knives > Bullets

4. Those dudes are ALWAYS oscar mike.

5. Gravity does not apply if you are on a snowmobile.

6. Never shoot from the hip, NEVER!

7. It's possible to speedrun the game in 3 minutes tops.

8. It has great soundtrack by Hans Zimmer. WHY NOBODY MENTIONED IT YET?

9. JOINT OPS

9. The heartbeat sensor cant determine if a enemy is up or down ....
 
 
10. If you have a bad ass mustache then you cannot die .

12.The most effective military tactic is rushing the enemy sporting dual P90's.

14....

10. A .50BMG might not be able kill a person, but a 9MM to the foot sure as hell can.

10.) Camping is always better for your health than moving.

11. Throwing knives always hit directly in the eye.

14. Stay out of the way of falling crates.

15. Two P90's is definitely better than one.

20. People don't number what they've learned right

16. You go into slo-mo when breaching a door.

18. Everybody smokes pot except me.( Well not anymore)

Lol this is some crazy dyslexic numbering shit in this thread .

It's because we are posting so quickly, lol.
 
(This is the number that we are at) 23. Call out "Star" when you want to know if a people in front of you are friendlies.

23. "Just switch to your sidearm, it's faster than reloading!"

People can control their blood temperature in exchange for having their guns do less damage.

21. Communication is key in hardcore team deathmatch.

22. It's extremely hard to settle on a single assault rifle that you can always go back to.

23. If you die enough time you can be stronger for 10 seconds

24.  Shepherd doesn't care about danger close or does he?.

32.  A grenade landing on grass sounds like a grenade hitting steel.
 
33. The counter-sign is Texas.
 
34. Americans are easily tricked into wars.
 
35. Gaz/Ghost are to Kenny as Modern Warfare is to South Park.
 
36.  Keith David's voice is the epitome of leadership.

39. Don't go to Brazil

40. Ghost opened the wrong door.

Strawberry jam is not helpful on the battlefield.

42. Heartbeat Sensor is your friend.

42.  Tourists are lied to about the President's bomb shelter.

" 6. Never shoot from the hip, NEVER! "

45. Don't be one of the F.A.G.S.

24. STOP FIRING FROM THE HIP! AIM DOWN THE SIGHTS 
- Gen. Shepard

Godammit. Everytime someone gets the number wrong I feel I have to write a new one with the correct number -_-
 
48. Ice picks to the chest is epic.

51. Don't go near windows if Captain Mactavish is chasing you.
 
@Mikemcn said:

" 50. Marines make the best Deep cover CIA operatives. "

I learned that not all Russians wear track suits.

53. Never trust a Russian Mercenary whore.
54. I am always the victim of grenade spam, all other players are repellent to them, must be a perk I don't know about.