OMGLOLWTFBBQ is composed of 4 abbreviations (OMG, LOL, WTF, and BBQ) and was originally used to make fun of people who used abbreviations online a lot. It can carry the meaning of any or all of the constituent abbreviations.
Three emotions, put into words, following eachother in quick succesion. Blunt Amazement, "Oh my God." Slight Amusement, "Laughing out loud." followed by Blank Confusion/Crude Amazement, "What the fuck?"
You are playing some sort of counter-strike like game. A friend of yours, or just someone you know, leaps over someone else's head(omg), looks down(lol), and plants a killing shot in his face(wtf?).
The best "ROFL" Phrase as of yet. First spotted on 4chan, it is sometimes used to describe Shoop Da Woop, the most ungodly awesome thing to visit this earth.