Look at the examples I provided. A direct quote (meaning a statement attributed to a specific individual) needs to be footnoted. "Do'h" by itself does not need citation. "Homer Simpson says 'doh' all the time." does not need citation. "When told that people on JWN are using him as a source for academic information, Homer Simpson's response was 'Do'h'" needs a citation.
We're also talking about use of copyrighted material here, if you're quoting from a copyrighted source, it needs citation; particularly in an academic environment.
If nothing else I can flunk you out my English class for not doing it the way I told you to, next semester you can find a prof that isn't as old as dirt and doesn't have OCD about this stuff.
edited to add: see "A Writer's Reference" Diana Hacker, Bedford/St. Martin's Boston, MA 1999 page 82