If someone replies with something that pisses me off, I just delete their reply and don't carry on the conversation. Most of the time I don't even bother reading their whole reply if I see that they're being intentionally mean. They probably think that they won the argument, which is just fine with me. That's why the internet is great: it's so easy to ignore the people that irritate you.
I stopped doing that myself. I stopped feeding them but as long as people do this sort of thing they are going to continue with arguing. I have been on other sites in the past where they would create alts just to argue with themselves. quite sad really, the right thing to do would be ignore them, walk away and not feed them. it's hard to do but it can be done.
The way I solve this problem is the way I solve every problem on the internet: add 3 grams of 'arguement is a waste of time' 2 grams of 'positive attitude towards people' 5 grains of salt and 15 grams of 'sense of humour'
if someone posts something I don't like, I may talk about it for a little while, but if it gets out of hand, well, find a plz account that will end or lighten the convo.
another method is to respond with a progression of faces or icons to each response they give. them: I think 32 degrees is a boiling point and you are dumb! you: them: my fish died at 32 degrees. do you think you are clever with your silly face? you're an idiot! you: them: I hate you! you are a poptart! you: them: UNCONTROLLED SWEARING you: them: i leave this conversation and/or develop a sense of humor.
or alternately, develop some catchphrases that end conversations.
example: i understand what you are saying you understand what you are saying. You're a very smart person etc.