I hated when homework was basically busy work, much like what sharky said above (actually basically his whole post is my gripe with school).

As far as more of a specific thing, there was this project that I had to do for Economics for a major portion of my grade at the end of my senior year in high school. You basically had to simulate living life fresh out of college. My partner and I picked a profession that would net us a good chunk of change to work with. Our teacher said it was too much and cut our salary in half. Now, I realized even then that sometimes people get underpaid, but our yearly income was barley above minimum wage.

But the worst part is how they actually made students to to insurance companies, car dealerships, etc. and simulate buying these things while providing proof (just have them print out a quote). It got to the point where many businesses (mainly car dealerships) refused to play along with the project anymore because they felt there were losing business to people who, you know, were actually at a place of business to buy a car, get a mortgage, buy insurance, etc.

The whole damn thing was a mess and I barely passed the class because of how poorly thought out that final project was.