I've heard people say Joe Dirt is classic, so it may be to some. I wouldn't argue that. Look at TCM (Turner Classic Movies) and all the movies that come on there. Not all of those movies are on IMDB 200 or classic lists, but they still are movies that we love and can watch anytime. I think that's what really matters when talking about classics. If you can still love it years later, then it can be a classic. Also, a movie that might be less loved in America may be loved in another country so the term classic will always be debatable.
Example:
I know Tropic Thunder was fake, but it made a good point that one mans trash is another mans treasure. Not everyone is a student of film, so even "bad" films can be classics to people that don't watch everything.