Ah, the online trash-talker, the scum of online play. They are usually not good at all, but think they are, this delusion fuels their over-inflated egos and drives them to trash talk anyone and everyone. All you can do is leave the server, mute them and/or add them to your block list.
Trash talkers tend to be low-middle level players as the better players usually just get on with it or leave. This usually can be used to combat them, if one has the energy and wit to do so. I had one tool in BF3 think he was hot shit because he was corner camping on Operation 925 with a Saiga killing then T-bagging my group after every single kill. He lost every game he played against us because we PTFO hard, yet he thought he 'beat' us because we 'won by points' (it was Conquest Domination, "winning by points" is the entire purpose). When I brought this up, he decided to brag about his K/D, (which according to Battlelog, is 1.5. Mine is over 2.) and when questioned, he said W/L didn't matter (in an objective based game). Trash-talkers are so much better when they own themselves for you.