For those who are new to this, here you go:
1. What are Social Justice Warriors?
Encyclopedia Dramatica Definition:
Social justice warriors are best described as a bunch of "activists" who sit around all day and bitch and moan about how everyone and everything is "racist/sexist/homophobic/transphobic/whorephobic/fatphobic/arachnophobic/bigoted/oppressive". They consider everyone who disagrees even in the slightest to be a "white hetero-cis scum", even if the ones disagreeing with them are ethnic minorities, gays, bisexuals, etc. Pretty much 99% of the time, social justice warriors on Tumblr never get the fuck off their ass and actually do something, as they're too busy telling people to "check their privilege" while at the same time not noticing their own privilege as they're able to afford a computer or their own innate hypocrisy as they will inevitably rage against well-off white cisgendered people all the while having a significant amount of well-off white cisgendered people making up their numbers.
In a simpler way, the main goal of SJWs is to try to promote equality, regardless of your gender, nationality etc. It may seem good, but a closer look at them in several websites (especially Tumblr (SJW's favourite site) and sometimes Twitter) will suggest otherwise - lots of sperging, ridiculous theories and moar for you to point and laugh at.
2. Common Terms Among SJWs
You can also find moar here: http://www.reddit.com/r/TumblrInAction/wiki/dictionary
If you want a head start without reading these, here you go, the most common terms used by SJWs on Tumblr:
Cisgender - Cisgender and cissexual (often abbreviated to simply cis) describe related types of gender identity where individuals' experiences of their own gender match the sex they were assigned at birth. (Source: Wikipedia)
Transgender - Transgender is the state of one's gender identity (self-identification as woman, man, neither or both) or gender expression not matching one's assigned sex (identification by others as male, female or intersex based on physical/genetic sex). (Source: Wikipedia)
Oppression - Basically a playing the victim card over criticism.
Otherkin - The belief that they are something else in a body of a human. An example would be a foxkin (Belief that you are a fox in a human's body).
Headmates - A person who describes themselves as having headmates is saying that they have people living in their heads who they have conversations with. Think of it as imaginary friends, but to SJWs they're real.
Trigger Warning - Usually shortened to tw. Used when something was used that "triggers" them when reading a certain post. Usually used for bullshit reasons most likely to shut down arguments.
Asexual - Not having a sexual attraction to anyone.
Genderfluid - Switching back and forth between identifying as a male or female.
Truscum - A term that is applied to anyone (but especially transgendered folks) who say that gender/sex dysphoria plays a key role in being trans.
Misogyny - Hatred of women.
Patriarchy - Belief that men control the society.
PoC - Person of Colour.
Rape Culture - The belief that rape is okay due to media.
Cultural Appropriation - Liking parts of a certain culture without identifying as a person from that culture.
3. So what do they complain about?
Everything. A game that doesn't have genders other than male and female? How people don't respect their genders? How a game is shaming fat people? They'll complain about them.
If they're not complaining, they'll sometimes ask people to respect their pronouns. Be sure to see them often as if you're using them wrongly, they'll complain about it as well.
4. My Preferred Tumblr Blogs to start with when following SJWs
http://wtfsocialjustice.tumblr.com/ - Documenting SJWs and their hilarious posts
http://everythingoffendsme.tumblr.com/ - My favourite satirical SJW Tumblr.
http://x-trung.tumblr.com/ - The most common SJW talked about here. A tortoisekin with lots of headmates. Though not active now, but still considered a favourite. Here's a notable post: http://x-trung.tumblr.com/post/27881827844/trigger-warning-singletism-ableism-fat-shaming