The Rickroll
To Rickroll is a tried and true troll tactic whereby the troll promises a link to something very exciting, such as an interesting video or obscene pornographic image, (ZOMG you hav to see this chick dude she tks two horses in teh ASS!!!11!!11LOL), but in reality said troll intentionally and willfully misdirects their unsuspecting victim to a video from 80's pop singer Rick Astley, usually and preferably the #1 hit single "Never Gonna Give You Up". This is considered your just and rightful comeuppance in regards to your personal desire to view material which is socially, morally, ethically and/or educationally vacuous, malicious or perverse.

This maneuver of annoyance gets its name in part from the 4chan 'duckroll', a similar but less musical imageboard misdirectional form, although both rolls have the same intent: ie: the pissing off of everyone by wasting their precious time through deliberate misdirection and deception. A Rickroll is not to be confused with the other famous rolls of the internet world, such as the before mentioned "duck", but should also not be confused with the Barrel, Drum, Let's, Egg, Rock n', or Dinner roll(s).

Rickroll Origin
Like everything else on the interbutts which is disturbing, illegal, annoying or sexually prurient, the origins of Rickrolling can be traced back to www.4chan.org, which is also known as the unofficial "asshole of the internet". You will never find a more wretched hive of scum and villainy. It was on the day of video game Grand Theft Auto 4's official website premier that the Rickroll spewed forth from one of 4chan's many rotting image birthing canals, the /v/ imageboard. Due to heavy traffic on the actual GTA4 website, it was impossible to watch the real game trailer for quite some time, so Anonymous took it upon himself to link everyone to a supposedly 'leaked' trailer hosted on YouTube. Internets hilarity ensued.

Anonymous
Later and somewhat ironically, some of the Internet Hate Machine itself, or the on-line group known collectively as "Anonymous", adopted "Never Gonna Give You Up" (along with Will Smith's soul-crushing theme from "The Fresh Prince Of Bel-Air") as one of the fighting anthems associated with the battle against the official tax exempt status of the scientology cult. These IRL protesting members of Anonymous are known as "moralfags", or people who are willing to retreat from lurking in their parent's basement, if only briefly, to take actual physical action on something that may have a moral or intellectual point, or an ethical goal. They will also be wearing an afro wig, or a black suit and tie and/or a Guy Fawkes mask from the graphic novel "V for Vendetta" just to make things moar interesting.

As for the rest of Anonymous, they (the "hatefags", which are actually the more traditional representation of the group), could care less about you or scientology or morality or good taste or humanity. They are a vile conglomeration of basement dwelling fucktards who celebrate, and actually revel in, the distribution of stomach-churning gore, infantile or illegal pornography, bestiality, or pictures of erect penises. They truly want nothing more than for you, or someone else in your family who may be sensitive and fragile, to end up inadvertently viewing GOATSE, GOOKSE, the pain series, shitting dick-nipples, lemon party, tubgirl or some animated gif file of a semi tractor-trailer running over an unlucky bicyclist. (Author's Note: I am embarrassed even bringing these terms up. Please do not pursue any of the before mentioned words in any search engine if you are in fact sensitive and/or fragile. Or if want to keep your lunch down. Or if you ever want to have a decent night's sleep ever again.)
b'dee, b'dee, b'dee, that's all folks, "Once you've seen it, you cannot unseen it."

Rickrolling Today
Rickrolling has now become very fashionable across the vast interwebs, and many, many sites now include some sort of Rickroll or variant for your old meme viewing pleasure. (You are here.) In fact, some people now surfing the web have stated that they actually enjoy being Rickrolled, and have, in what is now known to be the natural cycle of the internet, beaten the initially slightly amusing concept into a massive mainstream cluster-fuck of abstract failure. In response to this complacency, the now infamous and destructive RICKROLL//%VIRUS was developed by several gifted Eastern European computer hax0rs in a moving tribute to the original and relatively harmless Rickroll.

The Original Reaction To Being Rickrolled

Troll says: Dude, this video is so fucking WIN!!11! You have to check this shit out!
http://www.youtube.com/watch?v=oHg5SJYRHA0

(Unsuspecting victim returns after viewing Troll's "win" movie.)

Unsuspecting victim says: Dude wtf u rickroll'd me you stupid asshole :(

Troll says: lolz, fag. Enjoy your AIDS and complimentary music video Rickroll fgt.

Unsuspecting victim says: Dude fuck you. Blocked.

Unsuspecting victim has signed off. He/she will receive your messages once they sign in.

Troll says: LOL epic lulz/win.