Start up a match on Mega Lounge/Deathmatch, Duration 1 minute and Kill Limit 10. This can be in Player or Ranked matches, get your friend to search and when he joins quickly press Ready, a count down will begin and then the match will start. Now you either kill him 10 times or he kills you. You don't need to win you just need to Host the match and complete it without you're friend quitting the game.
Personally I boosted this in about an 1-2 hours, once you learn the map and meet up at the same spot after respawning it shouldn't take too long.
If you find this solution to be unhelpful, please tell me why in a comment and I will update it the next time I'm online.