E.g. flipping burgers at McDonald's isn't a shitty job because you're flipping burgers; it's a shitty job because you are paid badly, made to work much faster than it's healthy, and the management is shitty to you both personally and structurally, in how they plan the shifts, etc.

I'd argue that any shitty job could have a non-shitty variant with mostly the same tasks and responsibilities, and only the conditions changed. Which leads me to the answer to your question: anywhere between invention of agriculture and the industrial revolution, or perhaps even up to XIX century. Even when people toiled on farms, to then give most of it away to some nobles with swords, at least they weren't micromanaged day-in, day-out by said nobles.