It means "laughing my head off" and is in reference to an animated GIF of the beheading of American civilian Nick Berg by Iraqi terrorists.
It was popularized after 1justin (me) posted said GIF (created by takumi_) on a large LiveJournal community (indiefucks). Predictably, much drama ensued.
DON'T GET IN OVER YOUR HEAD lmho
115👍 110👎