I mean, obviously SJW types have always been around, but it's clear that the current type is more than anything a trend. There was a time when every other white middle class teenager on Twitter didn't have 'feminist' in their bios. Seeing people whine about white people was limited to certain corners of social media. Generally the attitudes of leftists before was "yeah racism is bad and Obama is a pretty cool guy." Now it's "WHITE PRIVILEGE! POC AND LGBT NEED TO BE REPRESENTED EVERYWHERE! CULTURAL APPROPRIATION! REEEEEEEEEEEEEEEE!"
Before people would be outraged when encountering genuine racism. Now they look for the most petty and trivial things to be outraged by.
From memory it was at some point between 2013 and 2015. I first heard the phrase 'social justice warrior' in 2015 but had started to notice these types becoming more and more common before then.
So what was the turning point? Occupy Wall Street? Ferguson? Gamergate? Maybe even the emergence of Trump himself?
TL;DR: See thread title.