Code:
This prx is automatic so once your In-Game, Press & Hold R+[] to Knife Everyone. 

#PRX OFF
0x00804FF4 0x00000001

To turn the prx off just add that code to your Datebase.

Add this line to game.txt in your seplugins folder

ms0:/seplugins/knife.prx

Enable in recovery and enjoy!!!
http://www.youtube.com/watch?v=7TElUhqq2NY

The link to download the prx
http://www.sendspace.com/file/vuy5kj