When No Means Yes

Late in life, after a series of strokes, Joseph Kennedy Sr. apparently lost all faculty of speech except for the word "No," which he then had to use to express a wide spectrum of emotions, including, often, approval and enthusiasm (i.e. "Yes").

Similarly, in Polish, "No" means "Yes" (or, more accurately perhaps, "Yeah," "Uh huh," "Yep," since "Tak" is the formal "Yes"). In Russian, it means "But." (Russian "Nu" is closer to Polish "No.") "Ja," which in German means "Yes," in Russian and Polish means "I"... etc. etc. etc.