In the original script, Alan was meant to have his beard shaved instead of his head, but Zach Galifianakis refused.
When filming the scene where Stu discovers the tattoo on his face, Bradley Cooper genuinely broke into laughter, and co-Writer and Director Todd Phillips decided to keep that take in the film.
Ed Helms (Stu) was severely sick from food poisoning when dancing in the street with no shirt on. After each take Helms would curl into a fetal position until it was time to film again.
Teddy's achievements closely resemble that of Ken Jeong, who took part on the High IQ team, played violin in the orchestra, was elected to student council, and graduated at 16.