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1.
The main character that you play in the Doom coputer games. The most l33t badass marine ever!
Man, did you see Doomguy blow master chief's gay ass with a rocket launcher?!?!?
by Spectre01 December 12, 2004
 
2.
A nameless yet awesome space marine from the 90's videogame DOOM. Impossibly manages to survive against hordes of alien space demon monsters from hell. That are evil. And scary. He also, for some reason knows how to use futuristic and experimental weaponry without training and can pwn demons with just a set of brass knuckles. A chainsaw helps, too.
"Yo, did you see that guy who just mugged that pedestrian? he just went all DOOM guy on him! Check out the brass knuckles!"

also, "the doom guy is badass."
guy 2 : "agreed"
by Dude Maximus June 15, 2010
 
3.
doomguy synonymous negative nancy, party pooper
person 1 "im really pumped about all the new stuff we're getting"

person 2 "whatever its not gonna make any difference i still hate everything about this"

person 1 *with the your any idiot look on his face*" don't be such a doomguy"
by Spoilscommunity May 29, 2010