A term used by arrogant twats to elicit an angered response from those they are referring to. It makes them feel superior to be one of the few truly "in the know".
It suggests that the peope being referred somehow have less education o a particular subject, follow only mainstream media, and are gullible. This of course is often a completely unsubstantiated claim.
1990's - You're fools! Global Warming will kill us all, but you're too busy consuming and polluting listening to whatever the news will tell you. ENJOY YOUR LIES SHEEPLE!
same person later
2000's - You're fools! There's no such thing as Global Warming! You're too busy listening to Al Gore and whatever these so called "green" companies say not realizing they're just after your money! ENJOY YOUR LIES SHEEPLE!