What is "whiteman's overbite"?

Rating: Null/10 (1 December 1998)

A story not only about love but about friendship of various kinds and about how people could overcome their self-consciousness. This may not be a date movie for some people, but it certainly gives hope on your marriage that you are desperately trying to hold on while at the same time wanting to let go every day.
So, what on earth does that "whiteman's overbite" mean, when Harry quotes it in the plane in front of 26 year old Sally? I'm serious. Please, somebody tell me.