This heading can be read both in the straightforward sense of 'rules about humour' and in the graffiti sense of 'humour rules, OK!' The latter is in fact more appropriate, as the most noticeable and important 'rule' about humour in English conversation is its dominance and pervasiveness. Humour rules. Humour governs. Humour is omnipresent and omnipotent. I wasn't even going to do a separate chapter on humour, because I knew that, like class, it permeates every aspect of English life and culture, and would therefore just naturally crop up in different contexts throughout the book. It did, but the trouble with English humour is that it is so pervasive that to convey its role in our lives I would have to mention it in every other paragraph, which would eventually become tedious - so it got its own chapter after all.
There is an awful lot of guff talked about the English Sense of Humour, including many patriotic attempts to prove that our sense of humour is somehow unique and superior to everyone else's. Many English people seem to believe that we have some sort of global monopoly, if not on humour itself, then at least on certain 'brands' of humour - the high-class ones such as wit and especially irony. My findings indicate that while there may indeed be something distinctive about English humour, the real 'defining characteristic' is the value we put on humour, the central importance of humour in English culture and social interactions.
In other cultures, there is 'a time and a place' for humour; it is a special, separate kind of talk. In English conversation, there is always an undercurrent of humour. We can barely manage to say 'hello' or comment on the weather without somehow contriving to make a bit of a joke out of it, and most English conversations will involve at least some degree of banter, teasing, irony, understatement, humorous self-deprecation, mockery or just silliness. Humour is our 'default mode', if you like: we do not have to switch it on deliberately, and we cannot switch it off. For the English, the rules of humour are the cultural equivalent of natural laws - we obey them automatically, rather in the way that we obey the law of gravity.