Continuity mistake: In the episode "FOX-y Lady" (7-10) it was established that Quagmire was 61 years old. In this episode, Quagmire stated to Meg he was bullied in 1986 and a flashback shows that he was a teenager. So how could Quagmire have been bullied in 1986 as a teenager if he should have been in his 30's at this time?
Character mistake: In the cutaway gag involving George and Lorraine McFly from "Back To The Future" Lorraine says she hasn't seen Marty from high school since prom. George, Lorraine and Marty all attended the Enchantment Under the Sea dance in November 1955, not the prom, which is usually held in May.
Continuity mistake: When Peter, Joe and Quagmire are watching Superman, they are first shown with three glasses on the table, one for each. After the scene of Superman is played on the TV, there are suddenly five glasses on the table.