The "Leave the gun, take the cannoli" bit.

When Clemenza makes a fool out of Michael who is at the phone with Kay, unwilling to tell her he loves her.

The whole Vitelli's scene when he realizes Michael and his men are talking about his daughter Apollonia.

When freshly engaged Michael and Apollonia are having a stroll, followed by a procession of women chaperoning them and by a couple of men, both with a lupara put on display.

Others will come to mind.