At the 3rd grade violin rehearsal ...
... Donnie Corleone Jr. walks in, opens his violin case and unveils, to the shock of all, a tommy gun. The teachers are livid, panic nearly ensues, but Donnie just starts laughing uncontrollably.
"What's wrong with you? This is serious! Why are you laughing?"
"Because I just imagined dad holding up the bank with my violin."