(1) One who is incredibly stupid or did something retarded. Combination of the words 'dumb' and 'pussy' or possibly a shortened 'dumbass'.
(2) Word coined by Strong Bad on [word]Homestar Runner[/word], used to make fun of Strong Sad.
> (1) "Jim, stop being a dumpus and hand me that screwdriver!"
> (2) "No misspellings + good idea + made fun of dumpus=SOLID!"