Joke for the Day.

'My Mother-in-Law fell down a wishing well. I was amazed, I didn't know they worked!'

This is a good example of the 'mother-in-law joke' in which the partner's mother is the butt (object/victim) of the joke. They seem popular in many cultures.

Jokes about mother-in-laws were traditionally told by men and are not as popular as they once were. They are associated with old-fashioned comedians.
To some they can be offensive and can now be seen as rather archaic. 

For more: http://www.motherinlawstories.com/mother-in-law_jokes_page.htm