I think he is the funniest character in the trilogy. Everything about him is amusing - his name, his appearance, his mannerisms... When young Vito is driving the truck full of dresses, and Fanucci pops up out of nowhere and goes "Eeeeehhhhh!"

I also like the hand signal that he uses. He does it a few times during the festival scene right before he gets shot. He sort of just holds up his right hand, like it's a gang sign for the Black Hand or something.

Funniest of all is Fanucci's death. After the first shot to his chest, he rips open his vest as if to verify, "Yup.. I've been shot." Then after the second shot to the face, he kind of freezes and hangs in the doorway for several seconds before collapsing in a comically theatric way.

Good old Fanucci.