This cheat is very complicated. You must do every detail right, so be very precise. Do not do anything in between, and that includes killing anyone else or getting killed.
Steps
1. Play multiplayer mode (4 player works best, I also suggest unlimited points and time) and select the map crossfire, I also suggest one or both of your opponents should have the deagle(or any other strong pistol, deagles are just better).

2. Track down the opponent that has the deagle (if they both have it, track down an opponent) and kill them with your main gun.

3. repeat step two twice after that, making sure you had killed them 3 times straight, without killing anyone else or being killed

4. Let them kill you with the deagle.

5. After being killed with the deagle, find a building with a trash can. If the trash can buzzes, it worked, if not, here are the biggest causes: 1, you got killed or went down 2, you didn't have 4 player on 3, they used a gun other than your pistol at any time, or 4, although this usually doesn't happen, you got shot by someone other than the target, or they shot you before the third kill.

6. Go to the top of the building, and a body will just fall through the city for no reason whatsoever