A study from the University of Warwick has shown that many British people are genetically predisposed to grumpiness.
The study of 131 different nations explains that having a shorter version of a certain gene (5-HTTLPR for those keeping track) "has been associated with higher scores on neuroticism and harm avoidance, stronger attentional bias towards negative stimuli, and lower life satisfaction."
The UK's population apparently has a high proportion of people with this shortened gene, which controls seratonin, a chemical affecting happiness.
This may be why Brits often make this face:
Not to be outdone by Brits, the French have an even higher percentage of their population with the ennui-producing short gene.
The Danes and the Dutch, meanwhile, have a lovely long version of the gene in question, making them irritatingly cheerful.
So the next time someone tells you to chin up, you can legitimately say to them, "Baby, I was born this way."
Or just scowl and ignore them.