Car insurance is definitely one I pay and think, "I 100% overpaying for this, but whatever I guess?" But is it the one I dread most? I'm sure a medical bill, if I had any, would be pretty terrible to regularly pay off...
The most egregious one for me is definitely rent. It's the bill that makes me feel most stuck. I pay it and think, "While that's absolutely essential so that I don't sleep outside, it's literally money I'll never see a dollar return on." It's legit 0.0% ROI, every month. So that's frustrating.
It's a good relentless reminder that I'm not really making forward progress.