Lewis Black's character says the word "fuck" twice, but one was literally bleeped out in order to make the movie PG-13.
A lot of the movie was improvised, and a lot of the gags were pitched by the actors on the day of shooting.
As part of the promotion for the movie at the Comicon in San Diego, promoters threw a huge "Welcome" party open to the public, with barbecue, beer, skateboarding demos, and a wall where people could write "subjects" they'd like to study. Justin Long and other cast members mixed in with the crowd, to the point that you couldn't pick them out.
(at around 1h 13 mins) Adam Herschman's actual parents were on hand during the "Parent's Day Scene," and were placed in the film as Glen's parents.
(at around 47 mins) The red fruits that Glen screamed "What are you!" at are rambutans, a kind of tropical fruit.