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1.
n.

1. One who plays Doom.

2. Ball shit snake.
"Doomers are ball shit snakes." ~ Username
by Holy Avenger May 03, 2004
 
2.
Someone who expects the worst possible outcome from a global occurrence, especially the peak in global oil production.

Antonyms are cornucopian, humanist, realist.

Doomers hold a faith based belief that humanity is incapable of resolving human-society created global issues, e.g. by replacing oil with other energy sources.

Refer apocophilia
peakoil.com is packed full of doomers practicing group-think like it was a survival skill.

I used to be a doomer, but then I remembered how to add.
by Jaymax September 16, 2005
 
3.
Someone who that revels in the thought of destruction of the planet or humanity due to global warming.

Antonym: denier.

Doomers hold an unshakable faith that the planet is inevitably doomed because of anthropogenic global warming and that nothing can reverse earth's ultimate destruction. In particular, doomers seem to take joy in discussing and contemplating a global doomsday.
The doomer took great joy in debunking a report that suggested that global warming doomsday predictions were exaggerated.
by Sierra Sam February 09, 2012
 
4.
n.

Used by the peak oil community to refer to those who believe that the end of the oil age will also mean the end of human society.
I'm a doomer 'cos wind and nuclear will never cut it, and hydrogen's a pipe dream.

You're doomerosity is only so high 'cos you're suffer from apocophilia.
by Justin Maxwell September 26, 2005