It's a pejorative term meaning "social justice warrior", almost invariably intended as an insult. In my experience, there's no well-defined meaning to the term (it covers a lot of ground), but it does send a pretty consistent message about the person using it.
There is also a pretty consistent message sent by identifying the term as pejorative and insulting, to be fair. There's a huge false dichotomy that holds that anyone who utters that phrase cannot possibly be progressive, when in fact the more likely scenario is that the speaker is progressive and is tired of a certain class of tactics overpowering the message.
This thread is exhibit A, to that end. Look how many people are up in arms about the shirt and have really lost the plot of what they're mad about, and still invest their lives arguing over the shirt months after it was dead and gone and the guy apologized, in response to a one line aside from the original commenter that was interpreted as permission to get opinions off chests. There's a person nearby fervently arguing about the shirt without even having seen the shirt, and yet we are supposed to accept that this is the best path to equality and progressive change?
I am not sharing an opinion (seriously, read my comment again), but I can tell from voting that it wouldn't matter anyway. My opinion would probably surprise the people voting on this comment, but I know better after several years than to ever speak to Hacker News about this topic and expect a coherent response. Again, I point to the thread.
I'm not sure that I know which way you mean that initial comment. I don't see there being any question that "SJW" is almost always intended as an insult: it's almost universally used by people who disapprove of that philosophy, and the term "warrior" is clearly meant as mockery. (I've occasionally seen folks say, "Why do they think that's an insult? I'd be proud to wear that label!" But that's a very different thing.)
I absolutely agree, though, that it also tells you things about the speaker when someone takes the time to speak up and say, "Hey, that term is used as an insult." (Disapproval of name-calling is only one of those things.)
Your error is the presupposition that it matters, and that we are indebted to you for gracing us with your speaking up about it. Misogynistic anti-progressives, as well as progressives who fetishize three letters and rail about their insulting properties, have nearly identical DNA when it comes to caring about self-image which is what it says about you.
Someone called you a SJW. Oh, no. What does it matter if you stay strong for what you believe? If you strongly believe in equality and comfortable environments for all, it will not matter what you are labeled or called, because you're above it. Soiling yourself with arguing about the term completely devalues whatever opinion you had. I see lots of people speaking up about the term "SJW," and I lose respect for every single one of their points of view. I'm not alone in that, based on conversations I have with people who don't take the time to subject their opinions to voting like this.
One can be progressive and distance themselves from much of the "SJW identity." The problem is that progressives like yourself would consider such a person moderate, and that's where you're disconnected from reality. I can tell that about you just based on the two comments I've read alone (especially your logical leap from one side of the colon to the other in your second sentence, that insulting a person implies beliefs), and I've trained that on far more people than yourself; I've also never been wrong. Yes, I've inferred a lot about you from what you're saying, but since I've never met you I cannot possibly be expected to behave otherwise.
Put another way, my biggest problem with the intersection of progressivism and the Internet these days is that both the SJW and anti-SJW camps have made everyone forget what the point of all of it actually is, and we're focused more on the failures of individuals like a shirt. The SJW-like progressives are just as complicit in that, but any opinion daring to say that is immediately seen as anti-progressive. Look at the effect: we're talking about an article of clothing months later.
Remember when I said my opinion would surprise you? Watch me hold these three simultaneously: I thought the shirt was mildly amusing, millions who have never met the person slamming him in public was unacceptable, and if it made someone in his workplace uncomfortable they should be empowered to speak up and all parties involved have a reasonable and productive conversation and potential behavior correction without fear of retribution.
Most people would read and understand all three. The current debaters would stop at the first one and rail me into oblivion. That's my problem. I'd call those people SJWs, and your initial comment which started this thread is that you can identify something about me based on that. Clearly, you cannot.
