For future reference most people on the EU forums dont like trophy boosters.. So try this forum instead -> http://www.ps3trophies.org
To be honest I don't see how this trophy is achievable unless you a). deliberately try to get it or b). have so many friends playing the game at the same time you somehow get in a game with just them Feel free to add me, after the madness that was the knife only match i hosted I still don't have it (turns out it doesn't work in private games)
Why i have 4 of my friends tags and i haven't deliberately tried to get it. ''sometimes'' when you join a friend and the other team has less players it puts you on the opposite side so i spent the whole game trying to find and knife my friends. I had a bad K/D ratio tho but it was easy, tense and fun to do.
Every time you play the game keep joining friends as one time you will end up playing each other.