I have to agree with EnzoBaker, that the Signor Roberto scene with Vito and Genco was entertaining. It was a complete role reversal with Roberto's added inability to open a door... Plus there was Genco's "He'll hide out in the Bronx" comment.

Some other funny scenes would have to be Michael's "true story" he told Kay about Johnny Fontane's contract.. It was also amusing when Vito was messing around with Johnny in his office.

Something oddly funny was also Luca Brasi's speach:

I am honored and grateful that you have invited me to your daughter's.. wedding... on the day of your daughter's wedding. And I hope that their first child be a masculine child....