Continuity mistake: After Jim Carrey crashes the car on the bridge and, we see in the long shots that the lamp on the half-broken post above him is swinging from side to side. However each time we cut to a closeup of Carrey's face, it is lit very evenly - although the only source of light nearby is swinging wildly.
Continuity mistake: When Pete awakes on the shore, the dog licking his face steps over his head, leaving footprints in the sand. In the following shots, however, the footprints have disappeared. (00:18:40)
Continuity mistake: When Jim Carrey's car goes into the water, it lands upside down. Then he is underwater and gets his coat off. The car is completely submerged at this point. When he comes up for air, the car is only halfway submerged with one of the ends sticking up perpendicular to the surface of the water.
Answer: Two possible reasons. 1. Hitting him back and telling everybody about Bob being a complete jerk would make him no better then Bob. 2. Bob actually knew the real Luke and if Peter had hit him, Bob could retaliate by telling everybody the truth.