It's suggested that increased ambient temperatures tend to increase aggressive behavior in humans. There is no generally agreed explanation.
See: ‘Ambient Temperature and Horn Honking : A Field Study of the Heat/Aggression Relationship’ in: Environment and Behavior, March 1986 vol. 18 no. 2 179-191.
A BBC 'Fact Check' feature (July 2018) lists various studies that confirm that there tend to be more reports of violent crime as the temperature rises.
“Experts divide the reasons into two main categories:
• The physical effects of heat on people's responses
• A change in the opportunities available to commit crime
Heat is an irritant and the discomfort it causes might make people shorter tempered. ”
Also see: Testosterone and aggression