2. One who is simply so stupid to be able to operate a disposable douch.
3. An incredibly irritating fuckwit.
'You're know you're a real douchetard, don't you?'
'Did you see that douchetard at the bar last night? I wouldn't have pissed on someone that annoying if their hair was on fire!'
(i.e., an asshole, jerk, jackass) and a "retard." Expresses both unpleasantness of personality AND stupidity at once.