The Mother-in-Law

Two guys were talking at work.
"I've got a problem," said the first one.
"What is it?"
"My wife has done it to me again. I'm supposed to buy my mother-in-law a present for her birthday, from the two of us. And I am fresh out of ideas. I mean it's HER mother, why can't she buy it?"
"What did you buy her last year?" the other one asked.
"Last year I bought her a VERY EXPENSIVE cemetery plot."
"Hmmmm, hard to top that one," said the other.
The two guys couldn't come up with anything. So the son-in-law didn't buy his mother-in-law anything for her birthday.
When the big day arrived the next weekend, she was a bit upset. At the family gathering for her birthday, she announced out loud to everyone, "Thank you all for the wonderful gifts. Too bad my daughter and son-in-law weren't so thoughtful!"
Thinking quickly, the son-in-law responded, "Well, you haven't used the gift I gave you last year!"