A euphemism for male masturbation. The humor in this euphemism comes from the fact that a quarter sized violin is roughly six inches (the length of a typical erect penis). Violin's are also "hard", "made of wood", and require careful "fingering". Vibrato (a common ornamental technique that requires a rapid back and forth movement of the hand along the neck of the instrument) could also be given new significance in the context of this metaphor.
by happystringguy April 30, 2010