We have been at that moment when we knife someone, only to watch the killcam and they knifed you while you barely began to swing.
Well, I think it would be a good idea to (when facing each other in a legitament counter active knifing zone) cancel knifing when 2 people knife in the same alloted amount of time (ie .5 sec).
Usually, I would say first come first serve. Or lag beat me. But lag in such close quaters needs to be able to have this affect. I've been on the good side of lag and the bad side, so I understand the situation.
What about guns and lag? I can't say anything about that, except to play more tactically when you are in that situation.
Plus, you can make an achievement (100x Knife cancellations).