Sorry if this joke has already been posted.....but as long as we're on the subject....
A friend of mine's wife is apparently going through the change of life. He bought her a mood ring so that he would have advance warning as to her mood changes.
Now, When she is in a good mood, the ring glows green
When she is in a bad mood, the ring glows black
And when she is having an especially bad day,
it leaves a red mark on his forehead.