My brother is doing some programming homework, and although it's in C++, which I don't really know, he keeps on showing me every function he writes, asking if I can tell what it is. One function, at one point, did this type of thing:
while a or b
do stuff to a and b
if a
do stuff
else
do different stuff
I realized something was wrong, and kept on telling him about it, and he was really thankful that I had caught it. He kept on thinking I was saying something else at first...