Revealing mistake: In at least one scene, you can see the ruts that the filmmakers made in the greens to make Happy's putts go where they wanted them to.
Revealing mistake: When Happy tosses the IRS agent out of Grandma Gilmore's window, he falls down the steps outside and it is blatantly obvious that he is wearing kneepads under his suit pants. (00:09:06)
Revealing mistake: In the scene where the Volkswagen is driving on the golf course to run over Happy, you can see tracks in the ground where the car had already been.
Revealing mistake: When Happy and Bob are rolling down the hill, you can see from the face that it's Bob Barker's stunt double. (00:57:05)
Revealing mistake: When Happy tees off at the AT&T Invitational, he swings his club about a foot above the ball, yet apparently he hits it successfully.
Revealing mistake: When Happy jumps on the alligator in the pond, it is very noticeably a rubber (fake) alligator.
Revealing mistake: When the car hits Happy you can see the flack jacket used to perform this stunt underneath his shirt. (01:14:07)
Chosen answer: He's the legendary golfer Lee Trevino.
Toolio