A more enlightened update of the incel. Where the incel is chronically alone, and projects his hatred onto women, the doomer has accepted his equally alone fate without resentment. Instead of bitching he listens to Radiohead on evening walks.
Usually in his 20s, the doomer is typically unemployed or doing a dead-end job, tormented by unrequited love, and alienated from most of the population; and this sense of personal aimlessness and despair seeps into his views on the world in general. So he lives in constant despair for humanity's future, with the prospect of ecological catastrophes and economic downturns tormenting his mind. To dull his sense of Weltschmerz he smokes, or drinks, takes drugs. But nothing can quite take away the dread that the doomer constantly feels towards the future. Hence his name.
He is the inheritor of a long tradition of being jaded with the world, and adopting this as a consistent worldview: he looks and nods at those that deny life: Hegesias of Cyrene, the Buddhists, Schopenhauer. But as a product of the modern world, he couldn't pretend that there is any ultimate spiritual redemption at the end. So he can only deny, deny, deny.
After she left him forever, he sat down, despondent and empty. But he mustered up the energy to put on his 90s playlist; and when the guitars from My Bloody Valentine's Loveless screeched their first note, he knew he was now a doomer.
Joder, soy un puto DOOMER.
El cuadro clinico de Urban Dictionary me diagnostica de forma exacta y fidedigna.