Although jokes about one's mother-in-law (the mother of one's spouse) are nowadays considered politically incorrect, they were once the mainstay of British comedians such as Les Dawson and Jim Davidson. The jokes are based on the idea that the mother-in-law considers the comedian to be unsuitable for her daughter, and that the mother-in-law is an ugly monster.
There is evidence that this joke dates back to Roman times. The writer Juvenal says that you can't be happy while the mother-in-law is still alive.
