its always gonna happen... there are always gonna be assholes on a site. he just needs to learn to deal with it and not to take it to seriously.
but as for your question... it usally means that the person that rep'd you didn't have enough points to give you a + rep so instead of giving you anything it gave you nothing. how much did my rep give you?
im at 7 points right now. thats counting the one you gave me.