This takes two people. Get your partner to host a private match and while in the lobby put your clan tag to read @.

Then tell your partner to make the game old school and make sure health is on double and regeneration is on fast.

Tell him to start the game while you have the clan tag screen up with @ in the field and when your are standing there with the countdown going on press start and the game will start normally.

Find a building that you have always wanted on top of.

Stand against the wall and jump, while in mid air press back (the scoreboard button) and a message will appear saying clan name contains illegal characters.

Do the exact same again and it will turn to a black screen saying this again - do not press anything.

You also have to make sure it is free for all.

This is where your partner comes in. Have him knife you 10-20 times leaving 6 or 7 seconds between each knife.

When he is finished press back again and you will fly way up in the air.

Just move towards the building and you should land on top of it.