Piano hands are when someone has very long and slim fingers that are highly agile and dexterous. If you have piano hands then you should learn how to play piano because it is the best instrument and you will become a amazing pianist.
The abnormally large hands of a musician, typically one who plays the piano. Can also pertain to the hands of a musician who plays an instrument requiring a wide physical reach such as guitar or bass. Note: hands must be freakishly huge and may only be called piano hands if the specimen is musically inclined. That's right, we know who you are, impostors. . .
Ususually used when trying to ignore a person in reaction to a comment made against the person, or a comment used to ask the person for something the person in question refuses to give
After being asked for a lift home) "my hand is a piano" (Then speakerwalks away)