An abbreviation of Social Justice Warrior, SJWs are people who believe or pretend to believe in "Social Justice" AKA ideas of white privilege, cis privilege, thin privilege, ableism, and patriarchy theory. This is often coupled by hatred for anyone who they consider "privileged" (cis people, white people, men, etc.) They're usually (but not always) white/Asian, upper-middle class females with a sexuality you have never heard of before. They will repeat the same mantra over and over, and will never change their opinion unless whoever is teaching them those ideas opinion changes. Their favorite phrase is "check your privilege." They use the website tumblr religiously.
White straight male: "hi"
SJW: "OMG HOW DARE YOU OPPRESS ME WITH YOUR WHITE MALE GAZE GET AWAY FROM ME YOU PIG! CHECK YOUR PRIVILEGE!"
White straight male: "All I said was-"
SJW: "STOP HITTING ON ME! STREET HARASSMENT! RAPE CULTURE! STOP RAPING ME!"
White straight male: "What are you talking abou-"
SJW: "WHITE DEVIL STOP RAPING ME YOU ABLEIST PIG!"
Another person: "no use in trying to reason with her, she's an SJW"
An alternative to saying "you're welcome" or "no problem."
"Hey man, thanks for helping me bury that body"
"Ain't no thang but a chicken wang"