Worst was a summer job as a laborer for a sandblasting company. Guys on scaffolds had long hoses used to sandblast a building, the sand fell to the ground, my job was to shovel it back into the machine so it could go up the hose again. Mindless, noisy, hot, backbreaking work.
I had an insane owner once but it wasn't the worst job ever. He was cheap, mean, stupid and two-faced, but as long as you didn't screw up you got to keep your low-paying job. I was by far the fastest typist there (part of the job was order entry), so he liked that there was no longer regular overtime to pay to the order entry people. When I quit, he offered me a raise that he flat-out told me was more than my manager was making and I had to be sworn to secrecy, while telling me I had a great future and was next in line for that manager's job. I didn't bother to mention that he just gave me a great reason why I wouldn't want to be the manager.
I'm pretty sure he thought being the owner meant he was automatically smarter than everyone else. He once, under the guise of "mentoring me", called me in and said I could go with him to a two-day conference about 300 miles away. It would have meant leaving the next morning, in the middle of a huge snowstorm. I said I had other commitments and could not go. He felt he was upping the offer by telling me I could drive his Cadillac. Yeah, the "mentoring" was nothing more than "be my chauffeur in a terrible storm for a few hundred miles."
Many skilled people would leave after a couple years and land much better jobs with our customers. Funny how he would bad-mouth everyone who left, implying that they were fired for not being able to cut it, then when they came in as customers he would fawn all over them. Just a 4-star idiot.