A self-righteous person acts superior to his peers because he believes his moral standards are perfect. This "moral smugness" is condescending by nature and is usually found offensive by others.
Self-righteousness is a way unintelligent and nonathletic people can retain a sense of superiority. Various cults and religions promote self-righteousness in an attempt to convert the average person, who feels immoral by comparison.
Joe: Hey, I downloaded this awesome movie! Want to go watch it?
Tim: You DOWNLOADED it?
Tim: *Sigh* That's immoral and against the law. I would never do that.
Joe: You're a self-righteous tool.
LOL BRIEFCASE is just a random thing that people yell because it's funny.
The origin is not certain, but the furthest I've been able to trace it is to a person named PsychicMaster on Warcraft III (Azeroth). He came into the Clan GS channel randomly and just yelled it. Then he'd leave.
PsychicMaster has joined the channel Clan GS.
PsychicMaster: LOL BRIEFCASE
PsychicMaster has left the channel.
This term originated in Warcraft III. While playing a custom map called Elimination Tournament, somebody died and yelled "LKAG," which was supposed to be "LAG." The server had not been lagging, and the message was supposed to be an excuse for being a n00b.
The term is usually used to make fun of a blatant excuse. It's a very condescending remark, much like lol internet and QQ.
Storm_Surge killed killer45 with the shotgun.
killer45: wtf omg lag!!1