The full moon makes people go crazy
My informant has heard since he was child that people go crazy on a full moon. Not everyone would go crazy but it would make the chance of encountering someone doing something crazy much more likely. People will drink too much or become stressed out and act aggressive or drive dangerously. My informant said that if he encountered a bad driver at night he would always check to see if it was a full moon because that could be the reason for it. He cannot remember where he originally heard the belief, but he said he has always grown up with it and it was treated as a fact.
The full moon comes only once a month and has always been a fairly important event. People have attached significance to those dates and it could be that because people expect others to act crazy on a full moon just makes them pay attention to events that they otherwise would just ignore as random. The belief could be true, but whether it is or not my informant said that he experienced events that made him a believer making the scientific proof of the matter not as important.
Annotation: This folk belief is the basis of the episode 13 “My Full Moon” in season 8 of the television series Scrubs. In this episode the doctors at the hospital have to deal with crazy patients on the night shift during a full moon.