I can't think of a single common synthesis that could be screwed up that badly.
Meh, we used to make nitroglycerin and pyrophoric lead - the favored bang stuff changes, but the urge of students to make it never does.
Back in spring 1972 I was a sophomore in high school and was in a chemistry class with 6 other boys(small rural school). The teacher was an older gentleman who had a heart attack in mid-March and the Principal forgot to get a sub to oversee us. Now get this....6 young men unsupervised in a fully equipped lab with the chemical storeroom unlocked.
Of the 6, 2 were seniors, one of those being the class valedictorian, 3 juniors containing both the valedictorian and the salutorian, and me, the future valedictorian of the Class of 1974.
Can you guess what happened very quickly?
Yes, we started with black powder, then nitro. It's a wonder we did not blow ourselves up, but after two weeks, the Principal stuck his head through the classroom door about 2 weeks later when he heard us doing one of the experiments listed in our textbook, saw the open storeroom door and quietly said "Oh my God!", trotted over to the teacher's lounge, and grabbed the only one in there, the football coach on a smoke break and told him to watch over us while he got a sub lined up....
We never told anyone about what we did until several years later when I was talking to the Principal (then retired) and told him what we did back then. He was not surprised by the revelation.....