Yancy's Saloon
Yancy's Saloon is a bar in San Francisco that is run by extortionists. It is the absolute worst bar you could ever hope to go to, especially if you wish to film an episode of Scam School.
Brian had booked an episode of Scam School to be filmed at this location on July 30, 2010. After they had started filming, Alan the bartender squeezed Brian for more cash. When Brian told him that they had no more cash, they were thrown out "with EXTREME prejudice!"
Following that, Brian sent out a tweet, alerting the demon hordes to the incident, linked to the bar's review page on Yelp, and said "you know what to do."
They did. In a period of several hours, dozens and dozens of negative reviews were left on Yelp. The venue's pages on Foursquare and Gowalla were also modified.
Aftermath
Yelp ended up removing many of the reviews from people not local to San Francisco, but a large number of negative reviews remain.
References
There is a building with boarded up windows on Chatrealm's Minecraft server in the South City region with a sign that says "Yancy's Saloon OUT OF BUSINESS". A sign on the rear indicates "Closed per order of Health Department"