What really pisses me off is that no one seems to know the difference between the words "then" and "than"
Then is used when there is an order involved. "First I eat, then I play video games."
Than is used as either a comparison, or in a conditional statement (aka, if, than statement). "My pen is bigger than yours", or "If I drink too much, than I will wake up with a hangover".
*edit: Apparently, my english 110 teacher was not entirely correct. I just checked this with the dictionary, and apparently the conditional statement "if, then" is infact then, and not than. Than is used in comparison, exception and conjunction.
but nevertheless, many people still use the wrong one in many cases.