Some of my favorite funny scenes:

-when Michael says to Connie in GFIII, "Maybe they should fear you!"
-Carlo gets tangled up in the curtains when he's giving Connie a beating
-the "Tony Bennett records" line
-"I don't care how many daigo, guinea, WOP, greaseball goombahs come out of the woodwork"
-Sollozzo's impatient glances at the waiter, and the look on his face when McClusky says, "Can't stand the aggravation" -- hilarious.