People like that are really what I hate most about this game. Unless you have the server first and glad there'll always be some dick who calls you bad and even then they might say you got carried/play an OP class or w/e. Just let it slide, 6/13 is above average and there are probably people out there who would like to switch places with you.
Next time that person says something to you just give him the "if you don't have anything nice to say, then don't say anything at all, bitch". Or put him on ignore, w/e.