A Viola is the world's smallest type of violin. Violins can only be as small as 11 inches in length according to traditional production methods. A Viola is by definition the worlds smallest violin as a Viola has been procuced at just 2 inches in length.
'Im playing the worlds smallest violin for you' in sarcasticly sympathetic reference to a mild misfortune someone encounters. This is a misnomer, you would actually be playing a (Viola).