Factual error: When the shop vac shoots the golf ball at Mr. Wilson's gonads, it only affects him for around ten minutes. The shop vac was able to shoot a glob of paint over 50 feet in the air so the speed and impact of the golf ball would have done much more than put Mr. Wilson in extreme pain for a short while. The impact would have likely caused internal bleeding, swelling, causing him to vomit, probably a rupture, requiring him to be hospitalized. There is no way he is walking away from that, he wouldn't even be walking at all.
Factual error: When Dennis uses the shop vac to clean up the paint he spilled, he takes the vacuum outside and flips the switch to "out" which the shop vac shoots a glob of paint into the air. In reality, the paint would actually ruin the fan inside the shop vac, causing it to jam.
Factual error: When Dennis's mom is outside Margaret's house and she is dragging Dennis inside, take a close look down the street. You can see Mr. Wilson's house and Dennis's house right next to Margaret's house. How is that possible if they drove to get there? (00:17:00)
Answer: Because of what George said to him in the house after he was robbed. He hurt Dennis' feelings so he ran away.