alt Hacker NewsI agree with your sentiment, but to answer your question: Since forever. (At least I know examples in the 90's).
In the old days of comp.lang.lisp, there were certain individuals who would really get off on denigrating people who wrote code that was not up to their ivory tower level. Some people left because of it. Others took it as a badge of honor falsely believing that the dressing down was necessary for them to improve their coding skills.
Example of an old discussion on HN about it:
Poorly socialized people tend to have poorly developed social mores.
And a lot of developers, especially on the internet, tend to be poorly socialized.
Salt that with the fact that they often are more fact-intelligent than the people around them in real life, and you get a propensity to shitpost whenever thry feel it's warranted, especially about technical things.