Stupidity: Jack has been using Mosley's badge and identification to pass himself off as FBI. He never once uses this trick to commandeer a civilian car for him and John when it would have been the safest way to get to L.A. much sooner.
Suggested correction: Probably because If he did that, the car's owner like Red the bar owner would eventually call the FBI office to get their car back and then the feds would know the make, model, license plate, and the last location of Walsh and the Duke. The police would have caught them in minutes. Walsh had to keep a low profile.
Stupidity: When Jonathan is chasing the truck to try and save Sarah, he could have removed his heavy backpack and run faster...but instead just leaves it on. No wonder he wasn't fast enough.
Stupidity: When Steve Martin reaches the beach with the wheelchair, he tips it over, giving the illusion that he fell out of it. However, with where he starts crawling on the beach, it's tipped the wrong way. If it was that way, he would've been on the other side of it. A clever con-artist should know better.
Stupidity: Paul Manfield (Arthur Pope) and his family have been hiding from and eluding the FBI for fifteen years, but Paul gets so intoxicated one night that he loudly sings "Pretty Woman" walking toward his house - where neighbors could hear - and yells that he is not Paul, he is Arthur Pope. (00:52:18)
Suggested correction: People do seriously stupid things when they are drunk, and Manfield/Pope is very, very drunk.