Mark Hurst of Good Experience interviewed New Yorker cartoon editor Bob Mankoff, who is working with the psychology department at the University of Michigan to research how humor works in the brain using cartoons as the input.
The experience of humor is similar to the "ah-ha" moment of two things coming together. For humor, two things have to come together to produce the experience of laughter. Normal and abnormal; these things reconciled in a moment, and usually it's a normal situation violated in some way that we can tolerate. You have to have something normal that becomes abnormal, or something that looks abnormal and then become normal.
So, normal: there's a guy on the phone, saying "No, Thursday's out. How about never – is never good for you?" Everything is normal – the office, the syntax of politeness – and yet the message is rude. We have a violation where we have a normal situation.