Someone whose pathetic work ethic is only matched by a complete lack of job skills.
There could be no more worthless an item in the universe than douche that's been used, so this should be reserved for those individuals who make one question the efficacy of evolution.
Can also be used in acronym form, SD.
"Dude, you didn't rack up the new server last week while I was on vacation!?"
"No, I couldn't find a cart so it's still in the mail room."
"DAMN... spent douche"