A Doomba is a death dealing floor cleaning robot. A Roomba (the popular floor cleaning robot) is outfitted with various dangerous items taped to it such as knives, cats, saw blades and blow guns.
"Dude what the fuck is that thing on your floor! It almost shanked me on my way in." "Oh dude, that's just my Doomba, it's a floor cleaning/home security robot, I'm going to enter him in Battle Bots next week"
The Doomba is excellent with getting away with its crimes as it cleans up after.