Following Rory's example, my worst job was working as a Telephone Harassment Flunky, otherwise known as a Market Researcher, at age 18. It wasn't the telephones we were harassing (although they probably didn't enjoy it much either), but the people on the other end of the line who were trying to eat microwave dinners in front of the TV with their broken families.
With such a glorious title as "Market Researcher" (I'm a scientist!) you would expect this job to have been rewarding and fulfilling, where I could go home and sleep well at night knowing I made a difference in the noble field of aggregate (made-up) consumer preferences. Reality was of course more like ruing my decision to commit myself to public disturbance for a meager paycheck.
The gist of the job was this: we would call people from a list of profiles and read to them survey questions, usually about commercial products, while goading them for truthful responses. The idea was to talk quickly and get a question in before they had a chance to say anything after "hello." Once we got started, people were less likely to refuse to participate. And with a question dangling in from of them, they'll usually just answer it.
Usually the questions were given to us on old WYSE dumb terminals with a fancy monochrome screen (all green letters on a black background, with the splash screen lettering firmly burnt into the phosphors). This was easy, as we could just key in the response and it would go to the next question automatically. But then there were the times when the computer network was broken (which was often), so we had to do the surveys the old-fashioned way--with pen and paper. Write down the response and turn to another page based on that response. You see, if the victim^H^H^H^H^H^H respondent hadn't used Colgate Extra Super Minty Professional with Bleach, we couldn't ask them if they liked how it made their gums glow in the dark, and how much they liked it measured on a scale of 1 to 10. All of this skipping around made it sort of like those Choose Your Own Adventure books. "If you'd like to call the respondent an asshole and hang up, turn to page 89!"
Every so often, I would get a person on the line that was very concerned with how I got their phone number, as if it were a secret code known only to them and Donald Rumsfeld. Although I had in front of me their name, address, medical history, and various other bits of personal information, we were told to say we were just dialing random numbers and theirs came up. Never mind that I might have asked for Mr. Yablome at the opening of the call. I don't think anyone ever noticed.
So what was your worst job ?