The most annoying debt (which I got rid of more than 20 years ago) was a credit card that had been canceled. I'd run up the debt with expensive car repairs and impulse purchases in grad school. Runner-up was the student loans I'd taken out in grad school so that I could do research (which I didn't really do that much of....totally could have worked instead.)
In short, it was all stuff I could have avoided with smarter budgeting and a little more effort, and they both took years to payoff. I've had debt since (cars, mortgages, student loans for an MBA) but at least I got tangible, useful stuff from those. Those early grad school debts sucked to pay back.