last semester in a calculus test, we had 5 problems (4 hard ones) and a "freebie" that required kowledge only of simple algebra.
So I spent almost all my time making sure I got the hard problems right. At the end of the easy problem I had something like 2x - x = answer.
For some reason I put -x as my answer. When we got out scores I had a 97 and 2 of the points were taken off because of my little mistake.
Some of my friends made a big deal about that so that became like my "own equation" so they would write that equation to refer to me.