What Could Have Been: MTV (who owns the rights to the name "Jackass") seriously considered making a Season 4 with all-new cast members and even put out a teaser commercial in the 2002 VMA Awards. Thankfully they didn't when reaction to the news was extremely negative.
Jackass: Too Hot For TV, which got killed when Lieberman started making noise against the show.
Bam's uncle was to be in Jackass 2 a great deal (you can see the original Lambo-tooth-pull in the trailer used against him), but a judge ordered all scenes relevant to him pulled off after being convicted of child molestation.
The Terror Taxi very nearly got here — they nearly got stopped by police twice, and Jay Chandrasekhar kept going off the rails (the police were told about the skit, but they still set up a damn roadblock), and two bystanders called the cops.
They were also about to attach squibs to the fake dynamite to scare Ehren more, but the Fire Marshall told them they had to more or less ruin the prank.