In 7th grade our teacher handed a paper out with a typo that said "Presidential erection" instead of "Presidential election".
A bit off topic but maybe a story worth telling...
Once in high school auto class, the teacher was ill and he left our sub a video for the class to watch out of his personal library. It was supposed to be something car related but it ended up being porn. Pretty funny mix up. Everyone was pissed when the sub wouldn't let us watch it.
Somewhat similar to a previous post, but one of my previous science classes we were studying natural rocks. One of them was called, well, "Schist". Some of my friends thought it was funny and all and began to chant it around as we laughed a bit. It was all fun and games...until one of us actually said, "S#@*" and wrote it on one of the tests. The irony of the situation was that he was one of the few that didn't really care for the "joke".
TL;DR S!*@ and Schist, know between natural rocks and feces.
Edit: So many grammar mistakes in my post, oh well.