I never read a book "surely you are joking mr Feynmann". But I was told where the title comes from. Feynmann was on some kind of event and they asked him if he wants milk or lemon in his tea. He was very shy and didn't know what was expected of him, so he said "both". In response they said "surely you are joking mr Feynmann".
Now, while it is assumed he said "both" simply because he was nervous, I think he actually got an excellent idea. I was actually drinking Feynmann tea every time we have a tea gathering in our school and I enjoy it. What happens when you put both milk and lemon into a tea is that lemon causes milk to clutter up. So basically you have pieces of cottage chease throughout your tea while the tea itself is mostly sour water with tiny bit of milk taste to it. So it "tames" a bit the sharp sour taste of lemon but at the same time it is still sour. Also it is a good and quick way of making buttermilk/cottage cheeze. So if you want to drink the latter you don't have to go to the store to buy it, you can just put a lemon into your milk.