Mine (erroneously missing from the list) would be:
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A Mathematician, a Biologist and a Physicist are sitting in a street cafe
watching people going in and coming out of the house on the other side of
the street. First they see two people going into the house. Time passes. After a while
they notice three persons coming out of the house.
The Physicist: “The measurement wasn’t accurate.”
The Biologists: “They have reproduced.”
Another person walks in.
The Mathematician: “Ah!”
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From the list, I also like 5, 24, and (meta-humor!) 42. A biologist, a chemist, and a statistician are out hunting. The biologist shoots at a deer and misses 5ft to the left, the chemist takes a shot and misses 5ft to the right, the statistician yells “… http://thoughtcatalog.com/2013/50-people-on-the-most-intellectual-joke-i-know/