Is it wrong to troll a troll?

So I pride myself on being one of the 'good' LoL players. I never flame a team mate no matter how bad a game they've had, I say well played to both teammates and opponents when they do something good, I never cry that I wasn't given blue or not ganked enough and if team mates are arguing I try and calm the situation down. The only exception to this is when I have a troll in my team, someone's who's acting like a spoilt child and is going out of their way to troll (afk farming, intentional feeding, offensive etc). At this point I go to town. I don't get offensive myself but I'll wind them up if I can, I'll ridicule them and undermine everything they say. If they 'mid or troll' I will take that lane to stop them getting their way (conversely I will always give a lane to the person who asks for it first politely). Is this acceptable behaviour or am I as bad as they are? I kinda see myself as a crusader defending the game from trolls but am I making things worse? Last night I had someone message me out of game to rage at me, 'Who the h*ll do you think you are' etc. I just saw this as validation that I'd got under his skin. What do you think?
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