This is trolling at its finest (or worst, really).
A MW3 player gets into a smack-talking back and forth with what seems to be a young kid, and records it for funsies. Funsies eventually turns into YouTube user Darknessgta4 playing the recording back to the kid, after which he actually gets the kid to argue with...himself.
The fact that the argument amazingly lines up so well just goes to show how ridiculous this whole trolling, online insulting thing really is. Can't we all just get by with a "good game" and leave it at that?