I'm glad the author mentioned this particular learning. Even if you do enjoy reading your own jokes, many other people will find them at best annoying and at worst confusing. When you add in people from other language/culture backgrounds the risk/reward of jokes gets even worse!
There was a famous conflict over rms's joke about the abort() function in the glibc manual[0], which said:
> Proposed Federal censorship regulations may prohibit us from giving you information about the possibility of calling this function. We would be required to say that this is not an acceptable way of terminating a program.
I think that joke illustrates nicely what I mean: it would only have made sense to people in USA, and would have just confused others. Even those who understood it would - IMHO - most likely not appreciate it being in the glibc manual. People don't read manuals to be entertained - they read them to find out as quickly as possible how to get their work done.