A new study, which has found a link between bad temper and the shape of a male's face, says that a man's aggression levels are written on his face.
Cheryl McCormick and Justin Carre from Brock University in Ontario, Canada, found that the larger the width-to-height ratio of a player's face, the more aggressive they were.
They measured aggression by the number of penalty points each player accrued for potentially harmful behaviour, such as elbowing and fighting.
In general, men's faces tend to have a larger width-to-height ratio than women's. This physical characteristic has been linked to higher levels of testosterone, which in turn is linked to aggressive behaviour, reports New Scientist.
Most people would not want to pick a fight with a big, brawny man, but because facial ratio is not linked to body size, it may have been favoured by evolution to warn others of an aggressive personality they would not want to tangle with.
Although the team first found the result in a study of students playing computer games, McCormick says they were "astounded to see that the measure could predict aggressive behaviour in a 'real world' setting".
McCormick's study raises the question of whether people can spot these subtle facial differences and use it to guide everyday behaviour.
"If someone was given the choice of one of two opponents to compete against who differed on the basis of the facial metric, would the facial metric predict the less aggressive opponent?" asks McCormick.
She believes that people's faces may be influencing who we chose to socialize with on a daily basis.
The study has been published in Proceedings of the Royal Society B.