Vigor

This game isnt really good but friendly fire is active so you can prank your friend shooting him. I did this with my friend about a year ago and it was fun. The game itself isnt that good, not much to do but at least you can have fun with your friends for a while, and it is also free so its nothing to lose. But if you want a game you can actually play for more than a week similar to this try Rogue Company or Warface(both free)