Well I found this website:
http://www.flug-revue.rotor.com/FRhe...04/FR9904e.htm
In August 1965 Joseph Sutter joined the team as Chief Designer. After the program launch in March 1966 Sutter and his team looked at 50 different designs with two decks. The double-decker design was not ideal, because passengers could not be evacuated in the time prescribed by the American Aviation Authority FAA. After viewing an improvised mock up of a cabin, which was uncovered, Trippe discarded the double deck idea. The view from the improvised top deck had given almost verybody present vertigo. It is obvious why everyone involved, apart from one Pan Am pilot, refused to use the attached emergency escape slide. After this sobering experience Trippe wanted to look at the 1:1 model of a conventional single deck, which was still being constructed. This design already had the famous hump, which was to be the trade mark of the 747. It goes without saying that the hunchback attracted many sarcastic comments. It was alleged that Boeing designed the hunchback to enable wealthy captains to sit on their thick wallets and not bump their heads.
There was a practical reason for the distinctive curve. Trippe had asked for the cockpit to be situated above the cabin. This was going to make loading easier. The space behind the cockpit was allocated to the air conditioning system and other instruments. However, businessman Trippe had other ideas. "This space is reserved for passengers. Couldn't we install a bar there?" Sutter agreed with this idea, but other ideas like glass nose for first class passengers only caused everyone to shake their heads. Impressed with the size of the cabin, there were many suggestions as to how to use it, i.e. a restaurant, cinema, hairdressing salon or even a casino.