The Bi-Monthly Science Fiction Convention or Bi-Mon-Sci-Fi-Con is the bimonthly science fiction convention held in the town of Springfield. The commercials advertise it with two aliens (implied to actually be Bill and Marty in costume) and the tag line "Be there...and be square!"
The convention is a magnet for the geeks, dorks and nerds of Springfield, and Lisa Simpson is quite unsettled when she is greeted by several boys (Milhouse, Wendell, Üter) from her school while there. Other attendees have included Dr. Hibbert, Lenny Leonard, Carl Carlson, Mayor Quimby, Mark Hamill (himself) and Matt Groening (himself in cameo appearance). ALF was also advertized to be an attendee at the convention.
Comic Book Guy has been seen at Bi-Mon-Sci-Fi-Con, and oddly is also involved in a romance in both times as well. The first time around he meets his female equivalent when sorting through boxes of, what else, comic books. However, when she requests that he comb the sweet tarts out of his beard, he dismisses her saying "Don't try to change me, baby." In the second time, the Simpsons go to the convention to prevent him from going any further in his relationship with Edna Krabappel. Edna had previously been a runaway bride at her and Skinner's wedding.
At one point, Neil Armstrong attempted to get a booth at the convention, but no one arrived to get autographs because, according to Edna Krabappel, no one cares that Armstrong had actually been to Outer Space, causing Neil Armstrong to hint at firing his agent afterwards.
Dr. Smith (or the actor portraying him) also arrived for the convention, although Bart doubts he's THE Dr. Smith as he's seen the movie. Dr. Smith mentions that he can clear it up by showing him his resume if Bart can accompany him to the food court, implying that he wanted to lure Bart away to molest him, but was foiled by the robot.
Besides meeting celebrities and looking at comics, another event advertized at the convention was the Tag Team Robot Wrestling, which once featured two Cylons from Battlestar Galactica versus C-3PO and R2-D2 from Star Wars (although R2-D2 did not actually participate in the match, even leaving when C-3PO needed help from the attacking Cylon). During this event, the contenders were referred to as "mighty" and "gay," respectively.
Even though Homer generally disliked nerds, he nonetheless went to the convention since it "beats work."